![2x^2-7x-4 \leqslant 0 \\ D=49+32=81 \\ x_1=\frac{7-9}{4}=-0,5 \\ x_2=\frac{7+9}{4}=4 \\ 2(x+0,5)(x-4)\leqslant 0](https://tex.z-dn.net/?f=2x%5E2-7x-4+%5Cleqslant+0+%5C%5C+D%3D49%2B32%3D81+%5C%5C+x_1%3D%5Cfrac%7B7-9%7D%7B4%7D%3D-0%2C5+%5C%5C+x_2%3D%5Cfrac%7B7%2B9%7D%7B4%7D%3D4+%5C%5C+2%28x%2B0%2C5%29%28x-4%29%5Cleqslant+0)
--(+)--(●-0,5)---(-)-----(●4)---(+)--->
![x\in[-0,5 ; 4]](https://tex.z-dn.net/?f=x%5Cin%5B-0%2C5+%3B+4%5D+)
Решение смотри на фотографии
Вроде так..
2sin²x-9sinxcosx+7cos²x=0 (:cos²x≠0)
2tg²x-9tgx+7=0
tgx=y;2y²-9y+7=0;y₁=1;y₂=7/2
1) tgx=1;x=π/4+πn,n∈Z
<span>
2) tgx=7/2;x=arctg(7/2)+πk,k∈Z.</span>
А) 5 - ( a - 3) = 5 - a + 3 = 8 - a
Б) 7 + ( 12 - 2b) = 7 + 12 - 2b = 19 - 2b
В) 64 - ( 14 - 7x) = 64 - 14 + 7x = 50 + 7x
Г) 38 + ( 12p - 8) = 38 + 12p - 8 = 30 + 12p = 6 ( 5 + 2p)