a) Với x = 0 thì ta được
\(\left(x^2-5\right)\left(x+3\right)+\left(x+4\right)\left(x-x^2\right)\)
\(=\left(0-5\right)\left(0+3\right)+\left(0+4\right)\left(0-0\right)\)
\(=-5.3+0\)
\(=-15\)
b) Với x = 15 thì ta được
\(\left(x^2-5\right)\left(x+3\right)+\left(x+4\right)\left(x-x^2\right)\)
\(=\left(15^2-5\right)\left(15+3\right)+\left(15+4\right)\left(15-15^2\right)\)
\(=220.18+19.\left(-210\right)\)
\(=3960-3990\)
\(=-30\)
c) Với x = -15 thì ta được
\(\left(x^2-5\right)\left(x+3\right)+\left(x+4\right)\left(x-x^2\right)\)
\(=\left[\left(-15\right)^2-5\right]\left(-15+3\right)+\left(-15+4\right)\left[-15-\left(-15\right)^2\right]\)
\(=220.\left(-12\right)+\left(-11\right).\left(-240\right)\)
\(=-2640+2640\)
\(=0\)
d) Với x = 0,15 thì ta được
\(\left(x^2-5\right)\left(x+3\right)+\left(x+4\right)\left(x-x^2\right)\)
\(=\left[\left(0,15\right)^2-5\right]\left(0,15+3\right)+\left(0,15+4\right)\left[0,15-\left(0,15\right)^2\right]\)
\(=-4,9775.3,15+4,15.0,1275\)
\(=-15,679125+0,529125\)
\(=-15,15\)
