cos 2A when sinA35Solutionfor using trigonometry formula cos

cos 2A when sinA=-3/5

Solution

for using trigonometry formula

cos 2A =cos²A-sin²A

              =1-2sin²A

              = 2cos²-1

Given that  

       sinA = -3/5

for using trigonometry formula cos2A=1-2sin²A

                                                             = 1-2(-3/5)²

                                                            =1-2(9/25)

                                                            =1-(18/25)

                                                           = (25-18)/25 .

                                                 cos2A= 7/25