Trig addition formula help

simplify:

cos75sin45+sin75cos45

Already I am stuck. If it were sin (a+b) then the equation would be in the form sinAcosB-cosAsinB

but we have cos as the leading term.

I thought that perhaps it would be cos(A-B)=but we have Cos then Sin on both sides.

Therefore in such a situation, would I be required to rewrite the equation to fit an appropiate formula, then calculate the values as normal?

(edited 9 years ago)

Reply 1

nerak99

13

Well since 75-45=30 you can work back to the a-b form and then you just need to state a very simple cos

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Reply 2

User1686961

12

Original post by apronedsamurai

simplify:

cos75sin45+sin75cos45

Already I am stuck. If it were sin (a+b) then the equation would be in the form sinAcosB-cosAsinB

but we have cos as the leading term.

I thought that perhaps it would be cos(A-B)=but we have Cos then Sin on both sides.

Sin(A+B)= sinAcosB+cosAsinB not minus you have got the equation wrong. Try again see if that helps. You can always change it to the way Sin(A+B) to make it easier to solve.

Reply 3

nerak99

13

Oh yes, well the fact that 75+45 = 120 gives you a simple sin to do

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Reply 4

User947387

OP

17

Original post by ThatGuyRik

Sin(A+B)= sinAcosB+cosAsinB not minus you have got the equation wrong. Try again see if that helps. You can always change it to the way Sin(A+B) to make it easier to solve.

So...I simplified the equation...to give me cos30+sin30

=

Is that correct?

Reply 5

TenOfThem

18

Original post by apronedsamurai

simplify:

cos75sin45+sin75cos45

Already I am stuck. If it were sin (a+b) then the equation would be in the form sinAcosB-cosAsinB

but we have cos as the leading term.

I thought that perhaps it would be cos(A-B)=but we have Cos then Sin on both sides.

Therefore in such a situation, would I be required to rewrite the equation to fit an appropiate formula, then calculate the values as normal?

ab = ba

Reply 6

User947387

OP

17

Original post by TenOfThem

ab = ba

Having a problem with my casio scientific calculator fx-991IES; its not simplifying surds....

is displayed as $\frac{ \sqrt{2} }{2}$

do I have it in the wrong mode or something?

(edited 9 years ago)

Reply 7

TenOfThem

18

Original post by apronedsamurai

Having a problem with my casio scientific calculator fx-991IES; its not simplifying surds....

$\frac{1}{ \sqrt{2} }$

is displayed as $\frac{ \sqrt{2} }{2}$

do I have it in the wrong mode or something?