# Triangle DEF is shown below. What is the measure of ∠D? Question
Right triangles and trigonometry Triangle DEF is shown below. What is the measure of $$\displaystyle∠{D}$$? 2021-01-11
The sum of the angle measures of a triangle is 180°. So, we write:
$$\displaystyle{m}∠{D}+{m}∠{E}+{m}∠{F}={180}°$$
$$\displaystyle{m}∠{D}+{57}°+{39}°={180}°$$
$$\displaystyle{m}∠{D}+{96}°={180}°$$
$$\displaystyle{m}∠{D}={84}°$$

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