Find the length of side x in simplest radical form with rational denominator

Find the area of the unshaded square

1yd 1 ft = 1 1/12 1 1/3 1 1/2 1 1/6

Which sum or difference identity would you use to verify that cos (180° - q) = -cos q? a.) sin (a -b) = sin a cos b – cos a sin b b.) cos (a -b) = cos a cos b – sin a sin b c.) cos (a -b) = cos a cosb + sin a sin b d.) sin (a + b) = sin a cos b + cos a sin b