20-20х-120=420
-20х=420-20+120
-20х=520
х=520/-20
х=-26
-5(0,6c-1,2)-1,5c-3 = -3c+6-1,5c-3 = -4,5c+3 = -4,5×(-4,9)+3 = 22,05+3 = 25,05.
Y=(x²+361)/x=x+361/x
y`=1-361/x²=(x²-361)/x2
x²=361
x=-19 U x=19
+ _ +
--------------(-19)------------(19)-----------------
min
ymin=y(19)=38