# Trig help

#1
I understand how to use them, but can someone clearly explain to me when to use all the different formulas in Trigonometry? (For e.g: how I can tell when to use Cosine rule)
0
4 years ago
#2
(Original post by chicchoc)
I understand how to use them, but can someone clearly explain to me when to use all the different formulas in Trigonometry? (For e.g: how I can tell when to use Cosine rule)
Cosine rule:
2 sides + enclosed angle to find opposite side
All 3 sides to find an angle

Sine rule:
Angle and opposite side + side to find the other opposite angle
Angle and opposite side + angle to find the other opposite side

Sine area rule:
To find area you need 2 sides + enclosed angle
To find a side you need the area + a side and the enclosed angle

In right angled triangles:
Sine:
To find angle you need opposite side + hypotenuse
To find hypotenuse you need angle + opposite side
To find opposite side you need angle + hypotenuse

Cosine:
To find angle you need adjacent side + hypotenuse
To find hypotenuse you need angle + adjacent side
To find adjacent side you need angle + hypotenuse

Tangent:
To find angle you need opposite side + adjacent side
To find adjacent side you need angle + opposite side
To find opposite side you need angle + adjacent side

1
4 years ago
#3
My revision guide described the trig rules quite well; I can post a photo of the explanation.
0
4 years ago
#4
(Original post by Loci Pi)
Cosine rule:
2 sides + enclosed angle to find opposite side
or 1 side, angle, and side opposite to the angle to find other side enclosing the angle.

Sine rule:
Angle and opposite side + side to find the other opposite angle
Angle and opposite side + angle to find the other opposite side

Sine area rule:
To find area you need 2 sides + enclosed angle
To find a side you need the area + a side and the enclosed angle

In right angled triangles:
Sine:
To find angle you need opposite side + hypotenuse
To find hypotenuse you need angle + opposite side
To find opposite side you need angle + hypotenuse

Cosine:
To find angle you need adjacent side + hypotenuse
To find hypotenuse you need angle + adjacent side
To find adjacent side you need angle + hypotenuse

Tangent:
To find angle you need opposite side + adjacent side
To find adjacent side you need angle + opposite side
To find opposite side you need angle + adjacent side

Not completely correct -

Cosine rule:
Three sides - use to get largest angle [oppostie largest side]
Are you sure about the seond use of cosine rule - draw a diagram as it doesn't sound correct.
1
4 years ago
#5
(Original post by Muttley79)
Not completely correct -

Cosine rule:
Three sides - use to get largest angle [oppostie largest side]
Are you sure about the seond use of cosine rule - draw a diagram as it doesn't sound correct.
You're right sorry I made a stupid mistake explaining it I will edit my comment.
0
4 years ago
#6
TSR won't let me upload the photo for some reason.
0
4 years ago
#7
(Original post by chicchoc)
I understand how to use them, but can someone clearly explain to me when to use all the different formulas in Trigonometry? (For e.g: how I can tell when to use Cosine rule)
The second post in the thread was incorrect but has now been amended.
0
4 years ago
#8
I have corrected the mistake now. The rest of it is correct though.
0
4 years ago
#9

Sine rule
0
4 years ago
#10

Cosine rule
0
4 years ago
#11

Sine area rule

You can ignore the fact that 'sine' is highlighted.
0
4 years ago
#12

Right angled triangles
0
4 years ago
#13
do you have any for c3 and c4 trig?
0
4 years ago
#14
(Original post by RuthieG101)
do you have any for c3 and c4 trig?
No, sorry. The most trig I know is C2 AS level but when I come to learning C3 and C4 diagrams like that would be useful.
0
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