Question

if cos is equal to 2 upon 5 find the value 4 + 4 ten square A

Answer 1

Hi friend,
Solution to your question is given in the picture attached. And do remember, it's tan not ten ( Had a hard time understanding your question ).
Hope my answer helped you

Answer 2

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let the angle be x since you have not provided
Cos x= 2/5
=>(Cos x)^2=4/25
=>1-(Sin x)^2=4/25
=>sin x = √21/5 or -√21/5
since
Tan x = Sin x/cos x
tan x =(√21/5)/(2/5)
tan x =√21/2
4+4tan x= 4+4×(√21/2)
=4+2√21
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by @strange