Question

Does anyone know how to do number 18????

Answer 1

Answer: angle ITU = 145 degrees

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Explanation:

Angle STU is the largest angle composed of the smaller angles STI and ITU.

In other words, the two smaller angles add up to the larger one.

(angle STI) + (angle ITU) = angle STU

( 20 ) + ( 12x+1 ) = 13x + 9

20+12x+1 = 13x+9

12x+21 = 13x+9

21-9 = 13x-12x

12 = x

x = 12

Using this x value, we find that,

angle ITU = 12x+1 = 12(12)+1 = 145 degrees

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As a side note,

angle STU = 13x+9 = 13(12)+9 = 165 degrees

This is confirmed with

(angle STI) + (angle ITU) = (20) + (145) = 165 = angle STU