Im pretty sure that it is 50
<h2>
Answer:</h2>
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<h2>
Step-by-step explanation:</h2>
<h3>1. Write the expression.</h3>

<h3>2. Substitute y for x, and x for y.</h3>

<h3>3. Solve for y.</h3>

<h3>4. Express your result.</h3>
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Answer:
C. 70°
Step-by-step explanation:
The inscribed angle marked 15° intercepts an arc that is double that measure, so the intercepted arc on the right is 2×15° = 30°.
The external angle marked 20° is half the difference of the intercepted arcs, so is ...
20° = (1/2)(x - 30°)
40° = x - 30° . . . . . . multiply by 2
70° = x . . . . . . . . . . . add 30°
The value of x is 70°.
The value of c for which the considered trinomial becomes perfect square trinomial is: 20 or -20
<h3>What are perfect squares trinomials?</h3>
They are those expressions which are found by squaring binomial expressions.
Since the given trinomials are with degree 2, thus, if they are perfect square, the binomial which was used to make them must be linear.
Let the binomial term was ax + b(a linear expression is always writable in this form where a and b are constants and m is a variable), then we will obtain:

Comparing this expression with the expression we're provided with:

we see that:

Thus, the value of c for which the considered trinomial becomes perfect square trinomial is: 20 or -20
Learn more about perfect square trinomials here:
brainly.com/question/88561