Question

第一题（21^2-11^2）^2 第二题（a+2）^2-(2a+1)^2 第三题（-3+a）^2(3+a)^2 第四题（

Answer 1

(21^2 - 11^2)^2

= [ (21 + 11)(21 - 11)]^2

= [ 32 × 10 ]^2

= 320^2 = 102400

(a + 2)^2 - (2a + 1)^2

=[ (a + 2) + (2a + 1)] [ (a + 2) - (2a + 1)]

= ( 3a + 3)( -a + 1)

= 3( a + 1)(1 - a)

= 3(1 - a^2)

= 3 - 3a^2

( -3 + a)^2( 3 + a)^2

= [ (a - 3)( a + 3)]^2

= ( a^2 - 9)^2

= a^4 - 18a^2 + 81

( x - y - 4) ( x + y + 4)

=[ x - (y + 4) ] [ x + ( y + 4)]

= x^2 - ( y + 4)^2

= x^2 - y^2 - 8y - 16