To work out the area of a triangle, you need to do (b x h) divided by 2. Therefore, you need to work out BE and AB. To work out BE, you need to use the information about the rectangle to help you.
Divide 98cm squared by 14 cm (DE) so find BE, so 7cm.
Also, you need to work out line AB to find the area. To do this, you need to use Pythagoras theorem.
You know that c squared = a squared + b squared (with c being the hypotenuse).
a squared = c squared - b squared.
a squared = 25 squared (i.e. AE) - 7 squared (i.e. BE)
a squared = 625 - 49
a squared = 576
a = the square root of 576
a = 24 cm
AB = 24 cm
So now we know the base and height of the triangle so we can apply the formula.
(b x h) divided by 2 = area
(24 cm x 7 cm) divided by 2 = area
168 cm squared divided by 2 = area
94 cm squared = area
Your final answer is 94 cm squared.
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