McGraw Hill Integrated II, 2012
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McGraw Hill Integrated II, 2012 View details
5. The Triangle Inequality
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Exercise 36 Page 450

Estimate the given roots using nearby perfect squares.

Yes, see solution.

Practice makes perfect

We are given square roots that we cannot calculate without a calculator. However, we can estimate their values using nearby perfect squares. First we will estimate the roots and then we can determine whether a triangle with the given side lengths is possible.

Estimating the Roots

Let's begin by considering the first given value, sqrt(3). We want to look for the perfect squares nearest to 3. Then we can compare their square roots in a compound inequality. sqrt(1)

Given root Nearby Perfect Squares Simplified Approximation
sqrt(3) sqrt(1) 1 sqrt(3)≈ 2
sqrt(15) sqrt(9) 3 sqrt(15)≈ 4
sqrt(24) sqrt(16) 4 sqrt(24)≈ 5

Can It Be a Triangle?

Now, using our approximated values, we can use the Triangle Inequality Theorem.

Triangle Inequality Theorem

The sum of the lengths of any two sides of a triangle must be greater than the length of the third side.

Let's verify if this theorem is true for these three roots. If yes, then it is possible to form a triangle with the given side lengths.

Approximated Side Lengths Triangle Inequality Theorem Simplified Inequality Is the Theorem Satisfied?
2 and 4 2+4? >5 6>5 Yes
2 and 5 2+5? >4 7>4 Yes
4 and 5 4+5? >2 9>2 Yes

Note that, all cases satisfy the theorem. Therefore, the given side length can be used to form a triangle.