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Zell_2famus
What is the length of DE?
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These triangles are similar (meaning they have the same 3 angles) you know this because the top angle is 40 deg, the two sides are = which means the triangle is isosceles, so its two base angles are equal (both are 70) the angles add up to 180: 40+70+70= 180 I would use proportions (or ratios) base is to side as base is to side 9 is to 12 as x is to 8 you can write that as: 9:12 :: x:8 or as ratios in fraction form: \[ \frac{9}{12}= \frac{x}{8} \] solve for x. one way is to multiply both sides by 8, then simplify