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would i use tangent for this 

 

http://prntscr.com/mhzppw

 Feb 7, 2019
 #1
avatar+28125 
+4

Use the cosine rule for this.

 

a2 = b2 + c2 -2bc*cos(A)

 

In your case 'a' is x, A is 62°, b is 2.0 and c is 2.5

.

 Feb 7, 2019
 #2
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but i cant use the cosine rule, i think i have to divide into two different 90 degree triangles

and then find the sides in the one with 62 degree inn and use sinus

sin62(1.8/2)= 0.79.....

2.5-0.79.... almost equal 1.7

then 1.7^2+1.8^2=6.148

sqrt(6.148)=2.479

but since i dont know if it was exactly 1.8 on the height then i might be at 2.4 cm

hmm

x=2.4

 Feb 7, 2019
edited by Guest  Feb 7, 2019
edited by Guest  Feb 7, 2019
edited by Guest  Feb 7, 2019
 #3
avatar+18840 
0

Why can't you use the cosine rule?   This question and diagram are a perfect set-up to use this rule......cheeky

ElectricPavlov  Feb 7, 2019
 #4
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but its before cosine rule

in the book

 Feb 7, 2019
 #5
avatar+18840 
-1

Where did you get the 1.8 from.....just a 'guestimate' ?     And if you use this value for the height, then

1.8/2   would equal sin 62 .....but you MULTIPLIED the sin  by sin 62......what does that do?    

ElectricPavlov  Feb 7, 2019
 #6
avatar+18840 
0

I think your book just got a bit ahead of itself in giving you this question before discussing the cosine rule.....

 

cos rule give answer as 2.357 units

ElectricPavlov  Feb 7, 2019
edited by ElectricPavlov  Feb 7, 2019
 #7
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i estimated the 1.8cm with a ruler

 Feb 7, 2019
 #8
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ok thank you!

 Feb 7, 2019

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