Bonjour,
1) Factorisation :
f(x) = 25x² + 30x + 9
f(x) = ( 5x )² + 2×5×3x + 3²
f(x) = ( 5x+3 )²
g(x) = ( x-2 )² - ( 6x+1 )²
g(x) = ( x-2+6x+1 ) ( x-2-6x-1 )
g(x) = ( 7x-1 ) ( - 5x-3 )
g(x) = - ( 7x-1 )( 5x+3 )
2) Factoriser h(x) :
h(x) = ( 5x+3 )² - ( 7x-1 )( 5x+3 )
h(x) = ( 5x+3 ) ( 5x+3-7x+1 )
h(x) = ( 5x+3 ) ( -2x + 4 )
h(x) = - 2 ( 5x+3 ) ( x-2 )