(3x - 4y)(3x + 4y) + (4y + x)(4y - 5x)
= 9x^2 - 16y^2 + 12xy + 12xy + 16y^2 - 20xy
= 9x^2 - 16y^2 + 24xy - 20xy
= 9x^2 + 4xy - 16y^2
-(5 - t/10)^2
= -(25 - 5t/10 + t^2/100)
= -(25 - t/2 + t^2/100)
= -25 + t/2 - t^2/100
( a+b)^2
= a^2 + 2ab + b^2
(5a - b)(b - 5a)
= 5a b - 25a^2 - b b + 5a * 5a
= 5ab - 25a^2 - b^2 + 25a^2
= -b^2 + 5ab - 25a^2
(3x - 4y)(3x + 4y) + (4y + x)(4y - 5x)
= 9x^2 - 16y^2 + 12xy + 12xy + 16y^2 - 20xy
= 9x^2 - 16y^2 + 24xy - 20xy
= 9x^2 + 4xy - 16y^2
-(5 - t/10)^2
= -(25 - 5t/10 + t^2/100)
= -(25 - t/2 + t^2/100)
= -25 + t/2 - t^2/100
( a+b)^2
= a^2 + 2ab + b^2
(5a - b)(b - 5a)
= 5a b - 25a^2 - b b + 5a * 5a
= 5ab - 25a^2 - b^2 + 25a^2
= -b^2 + 5ab - 25a^2