Question

if cosA=2/5 find the value of 4+4tan2A

Answer 1

Here,
cosA =2/5

now,we know that
tan2A = (1-cos²A) / (1+cos²A)

now 4+4tan2A =4 +4*{1-(2/5)²} / {1+(2/5)²}

=> 4+4{1- 4/25} / {1+4/25}
=> 4+4(25-4) / (25+4)
=> 4+84/29=(116 + 84) / 29 =200 /29 =6.89 answer

hope it helps ...