Isosceles trapezoid

Find the area of an isosceles trapezoid with bases of 8cm and 72mm. The height of the trapezoid is equal to three-quarters of the longer base.

Correct answer:

S =  45.6 cm²

Step-by-step explanation:

$$\begin{gathered} a=8\text{cm} \\ c=72\text{mm}\to \text{cm}=72:10\text{cm}=7.2\text{cm} \\ h=\frac{3}{4}\cdot a=\frac{3}{4}\cdot 8=\frac{3\cdot 8}{4}=\frac{24}{4}=6\text{cm} \\ S=\frac{a+c}{2}\cdot h=\frac{8+\frac{36}{5}}{2}\cdot 6=\frac{228}{5}{\text{cm}}^2=45.6{\text{cm}}^2 \end{gathered}$$

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