-3×25+7= -75+7=-68 ответ -68
A^loga b=b
5^(3+log5 2)=5^3*5^log5 2=5^3*2=125*2=250
X+y=1
x-3y=5
-4y=2
y=-2
x-2=1
x=2+1
x=3
S_10 = 80, а_5 = 6. Найти а_2 + а_4.
Составим систему.
{s_10 = (2a_1 + 9d)*10/2 {80 = (2a_1 + 9d)*5 ----> 2a_1 + 9d = 16
{a_5 = a_1 + 4d { 6 = a_1 + 4d ----> a_1 = 6 - 4d
2*(6 - 4d) + 9d = 16
12 - 8d + 9d = 16
d = 16 - 12
d = 4
a_1 = 6 - 4d = 6 - 4*4 = 6 - 16 = - 10
a_2 = a_1 + d = -10 + 4 = -6
a_4 = a_2 + 2d = -6 + 2*4 = -6 + 8 = 2
a_2 + a_4 = -6 + 2 = -4.
Ответ. -4
3^x • 3^y = 81
3^x + 3^y = 18
•••••••
3^x = a ; 3^y = b
ab = 81
a + b = 18
a = 18 - b
b( 18 - b ) = 81
18b - b^2 = 81
b^2 - 18b + 81 = 0
D = 324 - 324 = 0
b = 18 : 2 = 9
a = 18 - 9 = 9
••••••••
3^x = a
3^x = 9
3^x = 3^2
X = 2
3^y = b
3^y = 9
y = 2
Ответ ( 2 ; 2 )