Trapezoid MO-5-Z8

Trapezoid KLMN has bases 12 and 4 cm long. The area of triangle KMN is 9 cm². What is the area of the trapezoid KLMN?

Correct answer:

S =  36 cm²

Step-by-step explanation:

$$\begin{gathered} a=12 \\ c=4 \\ {S}_1=9 \\ {S}_1=c\cdot h\mathrm{/}2 \\ h=2\cdot S_1\mathrm{/}c=2\cdot 9\mathrm{/}4={\displaystyle \frac{9}{2}}=4.5 \\ S=(a+c)\cdot h\mathrm{/}2=(12+4)\cdot 4.5\mathrm{/}2=36{\text{cm}}^2 \end{gathered}$$

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