Question 1186673
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The triangles EDY and EFY are congruent by hypotenuse-leg, so angles DEY and FEY are congruent.<br>
So solve {{{2y+11=4y-7}}} for y to find the measure of angles DEY and FEY; then the measure of angle DEF is the sum of those two.<br><hr>
The student responded, saying that the diagram does not show that angle EFY is a right angle.<br>
He is absolutely right; I overlooked that.<br>
And that makes it impossible to answer the question.  Move point F along ray EF to different positions and the measure of angle DEF will change....<br>