# 4. Addition and Subtraction of Radicals

In algebra, we can combine terms that are similar eg.

2a + 3a = 5a

8x2 + 2x − 3x2 = 5x2 + 2x

Similarly for surds, we can combine those that are similar. They must have the same radicand (number under the radical) and the same index (the root that we are taking).

### Example 1

(a) 2√7 − 5√7 + √7

Answer

In this question, the radicand (the number under the square root) is 7 in each item, and the index is 2 (that is, we are taking square root) in each item, so we can add and subtract the like terms as follows:

2√7 − 5√7 + √7 = −2√7

What I did (in my head) was to factor out √7 as follows:

2√7 − 5√7 + √7

= (2 − 5 + 1)√7

= −2√7

(b) root(5)6+4root(5)6-2root(5)6

Answer

Once again, each item has the same radicand (6) and the same index (5), so we can collect like terms as follows:

root(5)6+4root(5)6-2root(5)6=3root(5)6

(c) sqrt5+2sqrt3-5sqrt5

Answer

In this example, the like terms are the √5 and −√5 (same radicand, same index), so we can add them, but the √3 term has a different radicand and so we cannot do anything with it.

sqrt5+2sqrt3-5sqrt5=2sqrt3-4sqrt5

### Example 2

(a) 6sqrt7-sqrt28+3sqrt63

(b) 3sqrt125-sqrt20+sqrt27

### Example 3

Simplify:

sqrt(2/(3a))-2sqrt(3/(2a)

### Exercises

Q1 sqrt7+sqrt63

Q2 2sqrt44-sqrt99+sqrt2sqrt88

Q3 root(6)sqrt2-root(12)(2^13)

Didn't find what you are looking for on this page? Try search:

### Online Algebra Solver

This algebra solver can solve a wide range of math problems. (Please be patient while it loads.)

### Ready for a break?

Play a math game.

(Well, not really a math game, but each game was made using math...)

### The IntMath Newsletter

Sign up for the free IntMath Newsletter. Get math study tips, information, news and updates each fortnight. Join thousands of satisfied students, teachers and parents!

Given name: * required

Family name:

email: * required

See the Interactive Mathematics spam guarantee.

### Algebra Lessons on DVD

Easy to understand algebra lessons on DVD. See samples before you commit.

More info: Algebra videos

Loading...
Loading...