16x^4-81y^4 difference of perfect squares...
(4x^2-9y^2)(4x^2+9y^2) that's one of the equivalents...
(2x+3y)(2x-3y)(4x^2+9y^2) that's another one of them...
Answer:
a. Radius of DA - 2 cm.
b. Area of rectangle ABCD -
c. Area of shaded - 8-4π
d. Perimeter of shaded region - also 8-4π
<em><u>Hope this helps! </u></em>