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Will mark brilliance

17. What is the value of y in ADEF?
D
7y +14
F
jo
9y+2
DE

Will mark brilliance 17. What is the value of y in ADEF? D 7y +14 F jo 9y+2 DE-example-1

1 Answer

1 vote

Answer:

y = 6

Explanation:

You want the value of y, given the sides of isosceles triangle DEF are marked as (7y +14) and (9y +2).

Isosceles triangle

The sides of an isosceles triangle are congruent, so we have ...

FD = FE

7y +14 = 9y +2

12 = 2y . . . . . . . . . . subtract 7y+2

6 = y . . . . . . . . . divide by 2

The value of y is 6.

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Additional comment

We know this triangle is isosceles for a couple of reasons. One is that the altitude is a perpendicular bisector of the base. Another is that the two smaller triangles are congruent by the SAS (or LL) postulate, making FD = FE by CPCTC.

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