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Nội dung: <blockquote data-quote="kieuyennhi" data-source="post: 70439" data-attributes="member: 69901"><p><strong>1 cách giải logic</strong></p><p></p><p><span style="font-family: 'Tahoma'">vi</span><span style="font-family: 'Tahoma'">ế</span><span style="font-family: 'Tahoma'">t pt đ</span><span style="font-family: 'Tahoma'">ườ</span><span style="font-family: 'Tahoma'">ng tròn qua các đi</span><span style="font-family: 'Tahoma'">ể</span><span style="font-family: 'Tahoma'">m A(1; 1); B(0; 2) và ti</span><span style="font-family: 'Tahoma'">ế</span><span style="font-family: 'Tahoma'">p xúc trong v</span><span style="font-family: 'Tahoma'">ớ</span><span style="font-family: 'Tahoma'">i đ tròn <img src="https://cdn.jsdelivr.net/gh/twitter/twemoji@14.0.2/assets/72x72/1f641.png" class="smilie smilie--emoji" loading="lazy" width="72" height="72" alt=":(" title="Frown    :("  data-smilie="3"data-shortname=":(" />x-5)^2 + (y-5)^2=16. (1)</span></p><p><span style="font-family: 'Tahoma'">Bài làm: </span></p><p><span style="font-family: 'Tahoma'">Gi</span><span style="font-family: 'Tahoma'">ả</span><span style="font-family: 'Tahoma'"> s</span><span style="font-family: 'Tahoma'">ử</span><span style="font-family: 'Tahoma'"> pt đ.tròn f</span><span style="font-family: 'Tahoma'">ả</span><span style="font-family: 'Tahoma'">i tìm: x^2 + y^2 + 2ax + 2by + c =0</span></p><p><span style="font-family: 'Tahoma'">Nó đi qua A và B nên ta có:2 + 2a + 2b +c =0 và 4 + 4b + c = 0</span></p><p><span style="font-family: 'Tahoma'">=> a = b + 1 và c = -4b - 4</span></p><p><span style="font-family: 'Tahoma'">=> m</span><span style="font-family: 'Tahoma'">ọ</span><span style="font-family: 'Tahoma'">i đ</span><span style="font-family: 'Tahoma'">ườ</span><span style="font-family: 'Tahoma'">ng tròn (1) đi qua A và B đ</span><span style="font-family: 'Tahoma'">ề</span><span style="font-family: 'Tahoma'">u có ph</span><span style="font-family: 'Tahoma'">ươ</span><span style="font-family: 'Tahoma'">ng trình d</span><span style="font-family: 'Tahoma'">ạ</span><span style="font-family: 'Tahoma'">ng: x^2 + y^2 + 2(b + 1)x + 2by - 4b - 4 = 0 (*)</span></p><p><span style="font-family: 'Tahoma'">Tr</span><span style="font-family: 'Tahoma'">ụ</span><span style="font-family: 'Tahoma'">c đ</span><span style="font-family: 'Tahoma'">ẳ</span><span style="font-family: 'Tahoma'">ng ph</span><span style="font-family: 'Tahoma'">ươ</span><span style="font-family: 'Tahoma'">ng (1') c</span><span style="font-family: 'Tahoma'">ủ</span><span style="font-family: 'Tahoma'">a 2 đ</span><span style="font-family: 'Tahoma'">ườ</span><span style="font-family: 'Tahoma'">ng tròn là đ</span><span style="font-family: 'Tahoma'">ườ</span><span style="font-family: 'Tahoma'">ng th</span><span style="font-family: 'Tahoma'">ẳ</span><span style="font-family: 'Tahoma'">ng:</span></p><p><span style="font-family: 'Tahoma'">(x-5)^2 + (y-5)^2 - 16 = x^2 + y^2 + 2(b + 1)x + 2by - 4b - 4 = 0</span></p><p><span style="font-family: 'Tahoma'"><=> 2bx + 2by + 12x - 10y -4b -13 = 0</span></p><p><span style="font-family: 'Tahoma'"></span><span style="font-family: 'Tahoma'">Đ</span><span style="font-family: 'Tahoma'">i</span><span style="font-family: 'Tahoma'">ề</span><span style="font-family: 'Tahoma'">u ki</span><span style="font-family: 'Tahoma'">ệ</span><span style="font-family: 'Tahoma'">n đ</span><span style="font-family: 'Tahoma'">ể</span><span style="font-family: 'Tahoma'"> 2 đ</span><span style="font-family: 'Tahoma'">ườ</span><span style="font-family: 'Tahoma'">ng tròn ti</span><span style="font-family: 'Tahoma'">ế</span><span style="font-family: 'Tahoma'">p xúc nhau là kho</span><span style="font-family: 'Tahoma'">ả</span><span style="font-family: 'Tahoma'">ng cách t</span><span style="font-family: 'Tahoma'">ừ</span><span style="font-family: 'Tahoma'"> O(0;0) đ</span><span style="font-family: 'Tahoma'">ế</span><span style="font-family: 'Tahoma'">n (1') b</span><span style="font-family: 'Tahoma'">ằ</span><span style="font-family: 'Tahoma'">ng R ( bkinh' đ.tròn(1) ):</span></p><p><span style="font-family: 'Tahoma'">d(O;(1')) = R</span></p><p><span style="font-family: 'Tahoma'"><=>|4b + 13|\ c</span><span style="font-family: 'Tahoma'">ă</span><span style="font-family: 'Tahoma'">n </span><span style="font-family: 'Tahoma'">ậ</span><span style="font-family: 'Tahoma'">c hai c</span><span style="font-family: 'Tahoma'">ủ</span><span style="font-family: 'Tahoma'">a(4b^2 + 4 b^2 ) = 4</span></p><p><span style="font-family: 'Tahoma'"><=> (4b + 13)^2 = 16.8b^2</span></p><p><span style="font-family: 'Tahoma'"><=> b = ..... (b có 2 giá tr</span><span style="font-family: 'Tahoma'">ị</span><span style="font-family: 'Tahoma'">)</span></p><p><span style="font-family: 'Tahoma'">Th</span><span style="font-family: 'Tahoma'">ế</span><span style="font-family: 'Tahoma'"> giá tr</span><span style="font-family: 'Tahoma'">ị</span><span style="font-family: 'Tahoma'"> c</span><span style="font-family: 'Tahoma'">ủ</span><span style="font-family: 'Tahoma'">a b vào pt (*) ta tìm đ</span><span style="font-family: 'Tahoma'">ượ</span><span style="font-family: 'Tahoma'">c2 đ</span><span style="font-family: 'Tahoma'">ườ</span><span style="font-family: 'Tahoma'">ng tròn th</span><span style="font-family: 'Tahoma'">ỏ</span><span style="font-family: 'Tahoma'">a mãn đi</span><span style="font-family: 'Tahoma'">ề</span><span style="font-family: 'Tahoma'">u ki</span><span style="font-family: 'Tahoma'">ệ</span><span style="font-family: 'Tahoma'">n bài toán.</span></p><p><span style="font-family: 'Tahoma'"></span></p><p><span style="font-family: 'Tahoma'"></span></p><p><span style="font-family: 'Tahoma'">_____________________CHÚC B   </span><span style="font-family: 'Tahoma'">Ạ</span><span style="font-family: 'Tahoma'">N H</span><span style="font-family: 'Tahoma'">Ọ</span><span style="font-family: 'Tahoma'">C T</span><span style="font-family: 'Tahoma'">Ố</span><span style="font-family: 'Tahoma'">T_______________________________</span></p></blockquote><p></p>

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