Question 1029748
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Assume quadrilateral ABCD is inscribed in a circle. If {{{m<A = x^2}}}, {{{m<B = 9x - 2}}}, and {{{m<C = 11x}}}, find x and the measure of angle D.
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If a quadrilateral is inscribed in a circle, then its opposite angles sum up to 180°.

In other words, If a quadrilateral is inscribed in a circle, then its opposite angles are supplementary.

I think if the teacher gave you this problem, you should be familiar with this fact. 
If not, you can read about it in the lesson <A HREF=https://www.algebra.com/algebra/homework/word/geometry/The-property-of-the-angles-of-a-quadrilateral-inscribed-in-a-circle.lesson>A property of the angles of a quadrilateral inscribed in a circle</A> in this site.

OK. Based on this fact, you can write an equation for the opposite angles A and C

{{{x^2 + 11x}}} = {{{180}}},   or

{{{x^2 + 11x - 180}}} = {{{0}}}.

Factor left side:

(x-9)*(x+20) = 0.

The only positive root is x = 9.

Hence, angle A is 81° and angle C is 11*9° = 99°. (which is not so important for us now).

What is really important, it is the fact that angle B is 9*9°-2° = 79°.

Then the opposite to B angle D = 180° - 79° = 101°.

<U>Answer</U>. Angle D has the measure of 101°.
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