Question

用配方法解下列方程(1)X^2-6X+4=0（2）X^2+5X-6=0 （3）2t^2-7t-4=0(4)3X^2-1=6X

代数 用配方法解下列方程 有过程
(1)X^2-6X+4=0
（2）X^2+5X-6=0
（3）2t^2-7t-4=0
(4)3X^2-1=6X

几何
分别写出图中 ∠A 、∠B的正值弦和余弦值：
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Answer 1

(1)X^2-6X+4=0
X²-6X+9-5=0
(X-3)²=5
X-3=±√5
X1=3+√5
X2=3-√5
(2)X^2+5X-6=0
X²+5X=6
X²+5X+(5/2)²=6+25/4
(X+5/2)²=49/4
X+5/2=±7/2
X1=-5/2+7/2=1
X2=-5/2-7/2=-6
(3)2t^2-7t-4=0
t²-7t/2-2=0
t²-7t/2+(7/4)²=2+49/16
(t-7/4)²=81/16
t-7/4=±9/4
t1=7/4+9/4=4
t2=7/4-9/4=-1/2
(4)3X^2-1=6X
X²-2X-1/3=0
X²-2X+1=1/3+1
(X-1)²=4/3
X-1=±√(4/3)
X1=1+2√3/3
X2=1-2√3/3

Answer 2

(1)X^2-6X+4=0
(x-3)^2=5,x=3±√5
（2）X^2+5X-6=0
(x+5/2)^2=6+25/4=49/4,x=-5/2±7/2，x=1或-6
（3）2t^2-7t-4=0
t^2-7/2t-2=0
(t-7/4)^2=2+49/16=81/16,t=7/4±9/4，t=4或-1/2
(4)3X^2-1=6X
x^2-2x-1/3=0
(x-1)^2=1/3+1=4/3，x=1±2√3/3

Answer 3

0.6，0.8
9/5，2/3

Answer 4

0=X^2-6X+3X^2-6
0=(x-3)^2-6
(x-3)^2=6
x-3=根号6
x=根号6=3

Answer 5

X^2-6X+4=0 (x-3)^2=5,x=3±√5
X^2+5X-6=0 (x+5/2)^2=6+25/4=49/4,x=-5/2±7/2，x=1或-6
2t^2-7t-4=0 t^2-7/2t-2=0 (t-7/4)^2=2+49/16=81/16,t=7/4±9/4，t=4或-1/2
3X^2-1=6X x^2-2x-1/3=0 (x-1)^2=1/3+1=4/3，x=1-2√3/3