Question

if cosA=3√2/5,then show that cos2A=11/25

Answer 1

Answer:

Step-by-step explanation:

Cos 2A = 2Cos² A - 1

             $= 2*(\frac{3\sqrt{2}}{5})^{2}-1\\\\=2*(\frac{3^{2}*(\sqrt{2})^{2}}{5^{2}})-1\\\\=2*\frac{9*2}{25} - 1\\\\=\frac{36}{25}-1\\\\=\frac{36}{25}-\frac{25}{25}\\\\=\frac{11}{25}$