# Two sides of an i

Given: two side of an isosceles triangle are 7x – y + 3 = 0 and x + y – 3 = 0 and its third side passes through the point (1, -10)

To find: third side of isosceles triangle

Explanation:

Let ABC be the isosceles triangle, where 7x y + 3 = 0 and x + y 3 = 0 represent the sides AB and AC, respectively.
Let AB = BC

Diagram:

AB = BC

tan B = tan C

Here,

Slope of AB = 7

Slope of AC = 1

Let m be the slope of BC.

Then,

Taking the positive sign, we get:

m2 – 8m + 7 = 7m2 + 8m + 1

Now, taking the negative sign, we get:

(m – 7) (m – 1) = - (7m + 1)(m + 1)

m2 – 8m + 7 = - 7m2 – 8m – 1

m2 = - 1 (not possible)

Equations of the third side is

y + 10 = - 3(x – 1) and

3x + y + 7 = 0 and x – 3y – 31 = 0

Hence, third side of isosceles triangle is 3x + y + 7 = 0 and x – 3y – 31 = 0

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