McGraw Hill Integrated II, 2012
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McGraw Hill Integrated II, 2012 View details
4. Rectangles
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Exercise 52 Page 511

Let's recall that the diagonals in a rectangle are congruent and bisect each other.

m∠APB=112^(∘)

Practice makes perfect

Let's begin with recalling that the diagonals in a rectangle are congruent and bisect each other. This means that DP=AP, and triangle DPA is an isosceles triangle. Therefore, m∠DAP=m∠ADP= 56^(∘).

As we know, in a rectangle all angles are right angles. Therefore, the sum of m∠DAP and m∠PAB is equal to 90^(∘).

56^(∘)+m∠PAB=90^(∘) ⇓ m∠PAB= 34^(∘) Again let's notice that, since diagonals in a rectangle are congruent and bisect each other, triangle APB is an isosceles triangle. This means that m∠ABP=m∠PAB= 34^(∘).

Now, as we are asked to find m∠APB we can use the Triangle Sum Theorem, which tells us that the sum of the measures of all angles in a triangle is always equal to 180^(∘). Let's substitute the measures of ∠PAB and ∠ABP.
m∠PAB+m∠ABP+m∠APB=180^(∘)
34^(∘)+ 34^(∘)+m∠APB=180^(∘)
68^(∘)+m∠APB=180^(∘)
m∠APB=112^(∘)
Therefore, the measure of ∠APB is 112^(∘).