X²-8x-84 = 0
a =1; b=-8; c=-84
D = b²-4ac
D = (-8)² - 4 · 1 · (-84) = 64 + 336 = 400 (√400=20)
x1 = -b+√D/2a ⇒ -(-8)+20/2 = 28/2 = 14.
x2 = -b-√D/2a ⇒ -(-8) -20/2 = -12/2 = -6.
2) 8(у²-6у+9)+15+40у-3у-8у²>2
8у²-48у+72+15+40у-3у-8у²>2
-11у+87>2
-11у>2-87
-11у>-85
у<85/11
4) 49z²-2z+1/49-(49z²-24.5z+22z-11)>0
49z²-2z+1/49-(49z²-2.5z-11)>0
49z²-2z+1/49-49z²+2.5z+11>0
0.5z+540/49>0
0.5z>-540/49
z>-1080/49
8^(1-log_4(x))=8/8^log_4(x)=8/2^3log_4(x)=8/x^(3/2)