Posted by **Anonymous- boy** on Friday, February 17, 2012 at 5:52pm.

in triangle ABC, the size of angle B is 5 times the size of angle A and the size of angle C is 9 degrees less than 4 times the size of angle A

Find the size of angle A

- algebra -
**MathMate**, Friday, February 17, 2012 at 6:09pm
You can set up the equations as follows:

B=5A

C=4A-9

A+B+C=180 (sum of angles of a triangle).

and solve for A, B and C.

However, you can easily solve it by substitution into the third equation:

A+B+C=180

A + 5A + 4A-9 = 180

10A=189

A=18.9

With A known, you can then find the remaining angles by substitution into the first two equation.

- algebra -
**MathGuru**, Friday, February 17, 2012 at 6:12pm
The sum of the angles of a triangle are 180 degrees.

Therefore:

Let x = angle A

5x = angle B

4x - 9 = angle C

Equation:

x + 5x + 4x - 9 = 180

Solve for x.

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