Bonjour,
----------------------------------------------------------------------------------------------------------
a) (x+5)² -21+2x = (x²+2*x*5+5²)-21+2x
= x²+10x+25-21+2x
= x² +12x + 4
b) 4(2x-3)² = 4(2x²-2x*2*3+3²)
= 4(2x²-12x+9)
= 8x²-48x+36
c) 3(t-2)²+1 = 3(t²-2*t*2+2²)+1
= 3(t²-4t+4)+1
= 3t²-12t+12+1
= 3t²-12t+13
d) -2(x+4)²-4x+7 = -2(x²+2*x*4+4²)-4x+7
= -2(x²+8x+16)-4x+7
= -2x²-16x-32-4x+7
= -2x²-20x-25
----------------------------------------------------------------------------------------------------------
Au plaisir d'avoir aidée :)