The longest side of an obtuse triangle measures 20 cm. The two shorter sides measure x cm and 3x cm.

Rounded to the nearest tenth, what is the greatest possible value of x?

6.3

6.4

7.0

7.1

If an obtuse triangle is given and 20 cm is the longest side, then:

x² + (3x) ² < 20²

x² + 9x² < 400

10x² < 400

x² < 40

x < 6.3

So, the greatest possible value of x could be 6.29999 ... ≈ 6.3 to the nearest tenth.