You are Here: Home >< A-levels

# mathematics watch

1. in triangle ABC, AB=-3i+6j and AC=10i-2j
a) find the angle BAC in degrees to 1 decimal place?

i have worked out that the magnitude of AB=3squareroot5 and the magnitude of AC=2squareroot3. now i dont knw what to do, can someone plz helppp??
2. use cos(theta)=a.b/mod(a)mod(b) formula
3. (Original post by Dan1999/17)
use cos(theta)=a.b/mod(a)mod(b) formula
I cant use as i dont knw what a is and i cant use a2 = b2 + c2 - 2bc cos A to work out a beacuse i dont knw what cosA is plus i cant use sine rule as i only knw 2 sides b and c

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: March 6, 2018
Today on TSR

### He lied about his age

Thought he was 19... really he's 14

### University open days

Wed, 25 Jul '18
2. University of Buckingham
Wed, 25 Jul '18
3. Bournemouth University
Wed, 1 Aug '18
Poll

## All the essentials

### Student life: what to expect

What it's really like going to uni

### Essay expert

Learn to write like a pro with our ultimate essay guide.

### Create a study plan

Get your head around what you need to do and when with the study planner tool.

### Resources by subject

Everything from mind maps to class notes.

### Study tips from A* students

Students who got top grades in their A-levels share their secrets