Sin^2x-cos^2x(sin^2x)=sin^4x

Please explain how to verify?

Which of the following of the following sets of side lengths could not form a triangle?

Can someone answer this question? : )

The magnitude, m, of an earthquake is defined to be m=log l/s, where i is the intensity of the earthquake (measured by the amplitude of the seismograph wave) and s is the intensity of a “standard” earthquake, which is barely detectable. what is the magnitude of an earthquake that is 1,000 times more intense than a standard earthquake? use a calculator. round your answer to the nearest tenth.