## A Maths Help~

PSLE marks the graduation of Primary school students and their entry into Secondary schools as teenagers. Discuss all issues about Secondary schooling here.

### A Maths Help~

Hi, I'm currently new here and need help with an A-Maths question. Can someone kindly help?

Without using a calculator, evaluate the value of:
cos(sin-1(-4/5)+tan-1(4/7))

P.S. -1 is inversed
sq is square root

Thank you.

Firehalk
KiasuNewbie

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### Re: A Maths Help~

Firehalk
KiasuNewbie

Posts: 2
Joined: Wed Feb 29, 2012 10:13 pm
Total Likes: 0

### Re: A Maths Help~

Firehalk wrote:Hi, I'm currently new here and need help with an A-Maths question. Can someone kindly help?

Without using a calculator, evaluate the value of:
cos(sin-1(-4/5)+tan-1(4/7))

P.S. -1 is inversed
sq is square root

Thank you.

Let x=sin-1 (-4/5), --> sin x =-4/5 (opp/hyp),
opp=-4, hyp=5, then adj=sq rt(5^2 - 4^2)=3

let y=tan-1 (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)
and sin y=opp/hyp=4/[sq rt(65)]

cos(sin-1(-4/5)+tan-1(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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