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Question
In the following figure, seg DH ⊥ seg EF and seg GK ⊥ seg EF. If DH = 18 cm, GK = 30 cm and `A(triangle DEF) = 450 cm^2`, then find:
1) EF
2) `A(triangle GFE)`
3) `A(square DFGE)`
Solution
1) Area of a triangle = 1/2 x base x height
`:. A(triangle DEF) = 1/2 xx EF xx DH`
`:. 450 = 1/2 xx EF xx 18` ......(Substituting the given values)
`:. (450xx2)/18 = EF`
`:. EF = 50 :. EF = 50 cm`
2) `triangle DEF` and `triangle GEF` have then common base EF
∴ their areas are proportional to their corresponding heights
`:. (A(triangle DEF))/(A(triangle GEF)) = "DH"/"GK"`
`:. 450/(A(triangle GEF)) = 18/30` ....(Substituting the given values).
`:. A(triangle GEF) = (450xx30)/18 = 750 cm^2`
`:. A(triangle GEF) = 750 cm^2`
3) `A(squareDFGE) = A(squareDEF) + A(squareGEF)` ....(Area addition postulate)
= 450 + 750 = 1200cm2
`:. A(squareDFGE) = 1200 cm^2`
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