A formula for calculating A, the area of a trapezoid, is A= 1/2h (b1+b2), where is h is the height of trapezoid, and b1 and b2 are the lengths of the parallel sides. What is A when h= 4 centimetres, b1= 10 centimetres, and b2 = 5 centimetres?

Given:  A = (½) * (b1 + b2) * h ;

→Multiply EACH side of the equation by "2", to get rid of the fraction, "½";

 → 2*A = 2 *  (½) * (b1 + b2) * h ;

 → 2* A = 1 * (b1 + b2) * h ;

 → 2A =  (b1 + b2) * h ;

→ Now, divide EACH side of the equation by: "(b1 + b2)" ; to isolate "h" on one side of the equation;

 →   2A  / (b1 + b2) =  [(b1 + b2) * h] / (b1 + b2) ;

 →   2A  / (b1 + b2) =  h ; ↔

The two parallel sides of a trapezoid are its bases. If we call the longer side b1 and the shorter side b2, then the base of the parallelogram is b1 + b2. Area of a trapezoid = 1 2 (base 1 + base 2)(height). A = 1 2 h(b1 + b2) The area of a trapezoid is half its height multiplied by the sum of its two bases.

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