If the coefficient of x ^ 3 in the expansion of (x-a / x) ^ 9 is - 84, then a= The known function f (x) = 2cos ^ 2x + sin ^ 2x-4cosx (1) find the value of F = (π / 3) (2) find the maximum and minimum of F (x)

If the coefficient of x ^ 3 in the expansion of (x-a / x) ^ 9 is - 84, then a= The known function f (x) = 2cos ^ 2x + sin ^ 2x-4cosx (1) find the value of F = (π / 3) (2) find the maximum and minimum of F (x)

Let R be x ^ 3
c(r,9) x^r (-a/x)9-r =-84x^3=c(r,9)x^(2r-9)(-a)^(9-r)
So 2r-9 = 3, r = 6
c(6,9)= c(3,9)=9*8*7/3*2*1=84 (-a)^3 *84=-84 a=1
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Let a = cosx (- 1)=

Solution equation: x ^ 2 + 3x-5 = 0

x²+3x=5
x²+3x+9/4=5+9/4
(x+3/2)²=29/4
x+3/2=±√29/2
x=(-3-√29)/2,x=(-3+√29)/2

The solution equation of the fifth grade: x-1.2-0.3x = 0.2

x-0.3x=1.2+0.2 0.7x=1.4 x=2

Solving equation 1 / x = x / (3x-2)

Convert x ^ 2 = 3x-2, X ≠ 0, X ≠ 2 / 3
X^2-3X+2=0
(x-2)(X-1)=0
x=2 X=1

X - | 2 / 3x + 1 | = 1 solution equation

x－|2/3x＋1|＝1
(1) 2 / 3x + 1 > = 0, that is, x > = - 3 / 2
x－(2/3x＋1)＝1
1/3x=2
x=6
(2)2/3x＋1

Solving the equation X-5 / 3x = 5 / 2
X-5 / 3x = 5 / 2

x-5/3x=5/2
0.4x=0.4
x=1

3x-2.4 = x to solve the equation

2x=2.4
x=1.2

Solving the equation (| a | - 1) x = a + 1 about X

① A ≥ 0 and a ≠ 1
（a-1）x=a+1
x=（a+1）/（a-1）
② A < 0 and a ≠ - 1
（-a-1）x=a+1
x=（a+1）/（-a-1）
x=-1
To sum up, x = (a + 1) / (A-1) or x = - 1 if a ≠ 1, a ≠ - 1

The solution of the equation a square x = 1-x of X is

1. A & # 178; - A & # 178; X = ax + 1-A & # 178; x-ax = 1-A & # 178; a & # 178; X + AX = A & # 178; - 1 x (A & # 178; + a) = A & # 178; - 1 when a = 0, the equation is: 0 x = - 1, no solution; when a = - 1, the equation is: 0 x = 0, the solution of the equation is any real number; when a ≠ 0 and a ≠ - 1, the solution of the equation is: x = (A-1) / A2

If the solution of the equation a (x-1) of X + a = - 5 / 4 is x = - 5 / 1, then a =?

x=-1/5
Substituting
(-1/5+a)/a(-1/5-1)=-4/5
Multiply by 5
(1-5a)/6a=-4/5
Take 30A on both sides
5-25a=-24a
a=5