# GCSE Maths help (lengths of a triangle)Watch

#1
In the triangle ABC
AC= 5CM
BC= 8CM
Angle ACB= 75 degrees

Calculate the lengh of AB

So I'm stumped. Its not trigonometry because there's no right angle, and its not Pythagoras?
Thank you
(Do you need a picture?)
0
7 years ago
#2
Use the cosine rule
0
7 years ago
#3
SinA/A = SinB/B

0
#4
To find the original value of x^2 you square it, how do you find the original value of x^3?
0
7 years ago
#5
To find the original value of x^2 you square it, how do you find the original value of x^3?
I'm perplexed, what do you mean? if that's what you mean.

As to the original problem, it's cosine rule.

In this particular method, , ,
and

Sub those in to the equation.
0
7 years ago
#6
It's definitely cosine rule, as you have two lengths and the angle between them
0
#7
(Original post by Stormwhite)
I'm perplexed, what do you mean? if that's what you mean.

As to the original problem, it's cosine rule.

In this particular method, , ,
and

Sub those in to the equation.
But I don't know the value of C, I tried I think I got 3 something... I rearranged the formula.
0
7 years ago
#8
But I don't know the value of C, I tried I think I got 3 something... I rearranged the formula.
What? No, no, where I've written BC and AC, they are the lengths. You are trying to find , you have , ,

Put those values into the cosine rule equation.
0
7 years ago
#9
Law of cosines.
0
7 years ago
#10
Cosine rule: http://www.math-mate.com/chapter60_2.shtml

That is how to use it.
0
7 years ago
#11
cosine rule

Spoiler:
Show
8.26cm
0
7 years ago
#12
To find the original value of x^2 you square it, how do you find the original value of x^3?
i think you're slightly confused.
Ok here, take an example.

5^2 = 25
original value is the square ROOT of 25 which is 5 right?

5^3 = 125
original value of 125 is the cube root this time. Cube root is basically finding the number that multiplies 3 times to get 125 - which is obviously 5, because 5 x 5 x 5 = 125
0
X

new posts
Latest
My Feed

### Oops, nobody has postedin the last few hours.

Why not re-start the conversation?

see more

### See more of what you like onThe Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

### University open days

• Cranfield University
Cranfield Forensic MSc Programme Open Day Postgraduate
Thu, 25 Apr '19
• University of the Arts London
Open day: MA Footwear and MA Fashion Artefact Postgraduate
Thu, 25 Apr '19
• Cardiff Metropolitan University
Sat, 27 Apr '19

### Poll

Join the discussion

#### Have you registered to vote?

Yes! (443)
37.83%
No - but I will (88)
7.51%
No - I don't want to (80)
6.83%
No - I can't vote (<18, not in UK, etc) (560)
47.82%