Question 1017069
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An equilateral triangle and a rectangle have the same perimeter. The length of a rectangle is 3 cm less tan twice the width. 
Each side of a triangle is 12 cm. find the area of the rectangle.
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The perimeter is 3*12 = 36 cm, calculated for the triangle.

The perimeter of the rectangle is the same: 36 cm.
So, the sum of the measures of two its consecutive sides is {{{36/2}}} = 18, which gives you an equation

x + y = 18.   (1)

It is the first equation. The second equation is 

x = 2y - 3,   (2)

according to the condition. Substitute the expression (2) into (1) to eliminate x. You will get

2y - 3 + y = 18,  --->  3y = 18+3 = 21  --->  y = {{{21/3}}} = 7 cm.

Thus one side of the rectangle is 7 cm long.

Then the other side of the rectangle is 18 - 7 = 11 cm.

Then its area is 7*11 = 77 {{{cm^2}}}.
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