Hi, I'm currently new here and need help with an AMaths question. Can someone kindly help?
Without using a calculator, evaluate the value of:
cos(sin1(4/5)+tan1(4/7))
The answer is 37/(5sq(65))
P.S. 1 is inversed
sq is square root
Thank you.
A Maths Help~
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Firehalk  KiasuNewbie
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Re: A Maths Help~
by Firehalk » Wed Feb 29, 2012 11:01 pm
Some one please help me, this is urgent...

Firehalk  KiasuNewbie
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Re: A Maths Help~
by mum_sugoku » Thu Mar 01, 2012 9:43 pm
Firehalk wrote:Hi, I'm currently new here and need help with an AMaths question. Can someone kindly help?
Without using a calculator, evaluate the value of:
cos(sin1(4/5)+tan1(4/7))
The answer is 37/(5sq(65))
P.S. 1 is inversed
sq is square root
Thank you.
Let x=sin1 (4/5), > sin x =4/5 (opp/hyp),
opp=4, hyp=5, then adj=sq rt(5^2  4^2)=3
hence, cos x = adj/hyp=3/5
let y=tan1 (4/7) > tan y=4/7 (opp/adj)
opp=4, adj=7, then hyp= sq rt(7^2+4^2) =sq rt(49+16)] =sq rt(65)
hence cos y=adj/hyp=7/[sq rt(65)]
and sin y=opp/hyp=4/[sq rt(65)]
cos(sin1(4/5)+tan1(4/7))
=cos (x+y)
=cosxcosy sinxsiny
=(3/5){7/[sq rt(65)]}  (4/5){4/[sq rt(65)]}
= 21/{5[sq rt(65)]} + 16/{5[sq rt(65)]}
=37/{5[sq rt(65)]}

mum_sugoku  BlueBelt
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