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Find the value of k so that the area of the triangle with vertices A(k + 1, 1), B(4, -3) and C(7, -k) is 6 square units.

Solution

✅ Correct Option: 1

Area =12∣x1(y2−y3)+x2(y3−y1)+x3(y1−y2)∣= \dfrac{1}{2}|x_1(y_2-y_3) + x_2(y_3-y_1) + x_3(y_1-y_2)|

=12∣(k+1)(k−3)+4(−k−1)+7(4)∣= \dfrac{1}{2}|(k+1)(k-3) + 4(-k-1) + 7(4)|

=12∣k2−6k+21∣= \dfrac{1}{2}|k^2 - 6k + 21|

Setting this equal to 6 gives k2−6k+21=12k^2 - 6k + 21 = 12, so k2−6k+9=0k^2 - 6k + 9 = 0 and k=3k = 3. The other case gives no real root.

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