✔ 最佳答案
1.設兩向量a.b的夾角為θ,且|a|向量=|b|向量,向量|a+b|=4 , 向量|a-b|=3,則cosθ=?
Set { } = 向量, c = cosθ, s = sinθ
Let {a} = (k, 0), {b} = (k*c, k*s) where k = waiting for determined
then {a} + {b} = (k(1+c), k*s)
and {a} - {b} = (k(1-c), -k*s)
|{a} + {b}| = k√[(1+2c+c^2)+s^2] = k√2(1+c) = 4
|{a} - {b}| = k√[(1-2c+c^2)+s^2] = k√2(1-c) = 3
divided:
4/3 = √(1+c)/√(1-c)
=> 16/9 = (1 + c)/(1 - c)
=> 9 + 9c = 16 - 16c
=> 25c = 7
=> c = 7/25 =answer
2.方程式(81x平方)=27分之根號3之解為何?
81x^2 = √3/27
x^2 = √3/(81*27)
x = +- ∜3/(9*3√3)
= +- ∜3*√3/(27*3)
= +- ∜3*∜9 / 81
= +- ∜27 / 81
= answer
3.設向量a=(cos60度, sin30度),向量b=(tan315度, sec120度),則向量a+b=?
{a} = (1/2, 1/2)
{b} = (-tan45, -sec60) = (-1, -2)
{a} + {b} = (-1/2, -3/2)
4.已知三角形ABC之三邊長為8,9,14,則向量
AB + BC + CA = 0 for a closed loop
5.設 0 <= X < 2π,則函數f(X) = cos²X - 3sinX + 2之最大值為?
We find max at point X = 270 deg by using of graphic method.
max = f(270 deg)
= cos²270 - 3sin270 + 2
= 0 + 3 + 2
= 5
= answer
6.y(x) = tan(x/3) 的週期為?
x/3 = π
=> x = 3π
=> Period = 3π = answer
7.設X為銳角,若sinX + cosX = 7/5,w = tanX + cotX = ?
7/5 = √2(sinX/√2 + cosX/√2)
= √2*sin(x + 45)
= √2*cos(X - 45)
=> sin(X + 45) = 7√2/10 & cos(X - 45) = 7√2/10
=> X = asin(7√2/10) - π/4 & X = acos(7√2/10) + π/4
Add:
2X = asin(7√2/10) + acos(7√2/10) = A + B
sin(2X) = sinAcosB + sinBcosA
= (7√2)^2/100 + [√(1-98/100)]^2
= 98/100 + 2/100
= 1
= sin90
=> 2X = 90
=> X = 45 deg
w = 1 + 1 = 2 = answer
8.若a2分之3平方乘a6分之5平方乘a3分之2平方=ax平方,其中a>0,則?
題意不明.無法演算
9.設 a > 0 且a不等於1,若 log<a>3 + log<a>7 = 3, 則 a = ?
3 = log3/loga + log7/loga
3*log(a) = log(a^3)
= log3 + log7
= log21
=> a^3 = 21
=> a = ∛21 = answer
10.若 log2 = a, log7 = b, 則log35等於下列何者?
(a) 1+a-b (b)1+a-b (c)1-a-b (d) 1-a+b
log35 = log5 + log7
= log(10/2) + log7
= log10 - log2 + log7
= 1 - a + b
= (d)
11.已知 x = 755度,則 x = 第幾象限?
x = 755 - 360*2
= 755- 720
= 35
= IQ
12.f(X) = 3sinX-2的最大值為?
-1 <= sinX <= 1
=> max = f(90 deg)
= 3 - 2
= 1
= answer
13.設A(-1, 4), B(2, 3), 則線段AB之垂直平分方程式為?
(x + 1)^2 + (y - 4)^2 = (x - 2)^2 + (y - 3)^2
2x + 1 - 8y + 16 = -4x + 4 - 6y + 9
answer: 6x - 2y + 4 = 0
14.在座標平面上,若兩平行線 L1: x + 2y = k 與 L2: x + 2y + 4 = 0
距離為根號√20且 k > 0, 則 k = ?
Point A = (0, -2) on L2
distance(A to L1) = |x + 2y - k|/√5
= |0 - 4 - k|/√5
= |k + 4|/√5
= √20
|k + 5| = 10
k + 5 = +-10
k = 10 - 5 = 5 = answer