Question

Quadrilateral ABCD is inscribed in a circle with m<A = (x2)°, m<B = (7x - 10)°,

and
m<C = (3x)°.
What is m<D?
​

Answer 1

106°

Explanation:

A quadrilateral inside a circle is a cyclic quadrilateral.

It means that the angles opposite are supplementary (add up to 180).

If we draw the quadrilateral ABCD, the angles A and C are supplementary and the angles B and D are supplementary.

Since we know A and C, we can write:

A + C = 180

x^2 + 3x = 180

x^2 +3x - 180 = 0

(x+15)(x-12) = 0

x= -15, or x = 12

Now, if we put x = -15, some angles become negative, so we disregard it and take x = 12.

Now finding B:

B = 7x - 10

B = 7(12) - 10

B = 74

We also know that B + D = 180, so:

B + D = 180

74 + D = 180

D = 180 - 74 = 106