Obtuse triangle is a triangle that has an angle that is greater than 90°.
longest side: 20 cm
two shorter sides: x cm and 3x cm
choice given: 6.3 6.4 7.0 7.1
Obtuse triangle Pythagorean Theorem
c² > a² + b²
20² > x² + 3x²
400 > 4x²
÷4 ÷4
100 > x²
10 > x
400 > 4(7.1)²
400 > 4(50.41)
400 > 201.64
The greatest possible value of x is 7.10