1,
$-2+6-12+16-22+26-...-92+96$
$=(-2+6)+(-12+16)+(-22+26)+...+(-92+96)$
$=4+4+4+...+4$
Nhận thấy, tổng trên có $10$ cặp số có giá trị bằng $4$
$→4.10=40$
2,
a, $(x^2-4)(x-5)=0$
$→$\(\left[ \begin{array}{l}x^2-4=0\\x-5=0\end{array} \right.\)
$→$\(\left[ \begin{array}{l}x=±2\\x=5\end{array} \right.\)
Vậy: `x∈{±2;5}`
b, $9-25=(7-3x)-(25+7)$
$→9-25=7-3x-25-7$
$→3x=-9+25+7-25-7$
$→3x=11$
$→x=\dfrac{11}{3}$
Vậy: $x=\dfrac{11}{3}$
c, $3x+7-9x=-11$
$→3x-9x=-7-11$
$→-2x=-18$
$→x=9$
Vậy: $x=9$
d, $3^4.(4x+16)=8.3^7$
$→324x+1296=17496$
$→324x=-1296+17496$
$→324x=16200$
$→x=50$
Vậy: $x=50$