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+0  
 
+2
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avatar+974 

The expression is \(4cos40cos50-4sin27.5sin17.5\) (in degrees.)

I got 0, with the following strategy

\(4[1/2(cos10+cos90)]-4[\frac{1}{2}(cos10-cos45)\)using product identities and then

\(2cos10+2cos90-2cos10-2cos90=0\)

But when I plug it in a calculator it shows up as \(\sqrt2\).

 

Help please?

Thank you very much!

:P

 Jun 15, 2019
 #1
avatar
0

Just wrong with the final term, which should be +2cos(45).

 Jun 15, 2019
 #2
avatar+104962 
+3

4cos (50) cos(40) - 4sin(27.5)sin(17.5)

 

2 [2cos(50) cos(40)  - 2sin (27.5)sin(17.5) ] =

 

2 [ cos (50 - 40) + cos (50 + 40)  -   [ cos (27.5 - 17.5)  - cos(27.5 + 17.5) ]  ]   =

 

2 [ cos(10) + cos(90)  - cos(10) +cos(45) ]  =

 

2cos(90)  +  2cos(45)  =

 

   0   +  2√2 / 2  =

 

√2

 

cool cool cool

 Jun 15, 2019
 #3
avatar+974 
+1

Thanks Chris!

CoolStuffYT  Jun 15, 2019

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