Find the perimeter of an isosceles triangle

whose base is 40 cm and whose base angle is 70".

whose base is 40 cm and whose base angle is 70".

\( cos70^o=\frac{20}{x}\\\\cos70^o\approx0.342\\\\\frac{20}{x}=0.342\\\\0.342x=20\ \ \ \ /:0.342\\\\x\approx58.5\ (cm)\\\\Perimeter:40cm+2\cdot58.5cm=157cm \)

\( cos70^0= \frac{20}{x}\\\\x= \frac{20}{cos70^0} \\\\the\ perimeter\ is:\\\\ P=2x+40=\frac{40}{cos70^0}+40 \ \ \ and\ \ \ cos70^0\approx0.3420\\\\P\approx\frac{40}{0.342}+40\approx156.96\ [cm] \)

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