[tex]\large\text{$ A ~medida ~da ~altura ~do ~ tri\hat{a}ngulo ~ \Rightarrow ~ h = 12 ~cm$}[/tex]
[tex]\large\text{$ Rela\c{c}\tilde{a}es ~m\acute{e}tricas ~do ~tri\hat{a}ngulo ~ret\hat{a}ngulo $}[/tex]
Encontrar a medida do cateto.
[tex]c = \dfrac{3}{4} ~. ~20\\\\\\c = \dfrac{3 ~. ~20}{4} \\\\\\c = \dfrac{60}{4} \\\\\\c = 15 ~cm[/tex]
Com as medidas dos catetos encontrar o valor da hipotenusa.
[tex]a^2 = b^2 + c^2\\\\a^2 = 20^2 + 15^2\\\\a^2 = 400 + 225\\\\a^2 = 625\\\\a = \sqrt{625} \\\\a = 25 ~cm[/tex]
Encontrar o valor da altura ( h ).
[tex]bc = ah\\\\20 ~. ~15 ~= 25h\\\\300 = 25h\\\\h = \dfrac{300}{25} \\\\\\h = 12 ~cm[/tex]
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