第 12 类 NCERT 解决方案 – 数学第一部分 – 第 5 章连续性和可微性 – 练习 5.5 | 2套
第5章连续性和可微性——练习5.5 |设置 1
问题 11. 关于 x 对函数进行微分。
(x cos x) x + (x sin x) 1/x
解决方案:
Given: (x cos x)x + (x sin x)1/x
Let us considered y = u + v
Where, u = (x cos x)x and v = (x sin x)1/x
So, dy/dx = du/dx + dv/dx ………(1)
So first we take u = (x cos x)x
On taking log on both sides, we get
log u = log(x cos x)x
log u = xlog(x cos x)
Now, on differentiating w.r.t x, we get
………(2)
Now we take u =(x sin x)1/x
On taking log on both sides, we get
log v = log (x sin x)1/x
log v = 1/x log (x sin x)
log v = 1/x(log x + log sin x)
Now, on differentiating w.r.t x, we get
………(3)
Now put all the values from eq(2) and (3) into eq(1)
找出问题 12 到 15 中给出的函数的dy/dx
问题 12. x y + y x = 1
解决方案:
Given: xy + yx = 1
Let us considered
u = xy and v = yx
So,
………(1)
So first we take u = xy
On taking log on both sides, we get
log u = log(xy)
log u = y log x
Now, on differentiating w.r.t x, we get
………(2)
Now we take v = yx
On taking log on both sides, we get
log v = log(y)x
log v = x log y
Now, on differentiating w.r.t x, we get
………(3)
Now put all the values from eq(2) and (3) into eq(1)
问题 13. y x = x y
解决方案:
Given: yx = xy
On taking log on both sides, we get
log(yx) = log(xy)
xlog y = y log x
Now, on differentiating w.r.t x, we get
问题 14. (cos x) y = (cos y) x
解决方案:
Given: (cos x)y = (cos y)x
On taking log on both sides, we get
y log(cos x) = x log (cos y)
Now, on differentiating w.r.t x, we get
问题 15. xy = e (x – y)
解决方案:
Given: xy = e(x – y)
On taking log on both sides, we get
log(xy) = log ex – y
log x + log y = x – y
Now, on differentiating w.r.t x, we get
问题 16. 找出由 f(x) = (x + 1)(x + x 2 )(1 + x 4 )(1 + x 8 ) 给出的函数的导数,从而找到 f'(1)。
解决方案:
Given: f(x) = (x + 1)(x + x2)(1 + x4)(1 + x8)
Find: f'(1)
On taking log on both sides, we get
log(f(x)) = log(1 + x) + log(1 + x2) + log(1 + x4) + log(1 + x8)
Now, on differentiating w.r.t x, we get
∴ f'(1) = 2.2.2.2.
f'(1) = 120
问题 17. 用下面提到的三种方法区分 (x 5 – 5x + 8)(x 3 + 7x + 9)
(i) 通过使用乘积规则
(ii) 通过展开乘积得到单个多项式
(iii) 通过对数微分。
他们都给出相同的答案吗?
解决方案:
(i) By using product rule
dy/dx = (3x4 – 15x3 + 24x2 + 7x2 – 35x + 56) + (2x4 + 14x2 + 18x – 5x3 – 35x – 45)
dy/dx = 5x4 – 20x3 + 45x2 – 52x + 11
(ii) By expansion
y = (x2 – 5x + 8)(x3 + 7x + 9)
y = x5 + 7x3 + 9x2 – 5x4 – 35x2 – 45x + 8x3 + 56x + 72
y = x5 – 5x4 + 15x3 – 26x2 + 11x + 72
dy/dx = 5x4 – 20x3 + 45x2 – 52x + 11
(iii) By logarithmic expansion
Taking log on both sides
log y = log(x2 – 5x + 8) + log(x3 + 7x + 9)
Now on differentiating w.r.t. x, we get
dy/dx = 2x4 + 14x2 + 18x – 5x3 – 35x – 45 + 3x4 – 15x3 + 24x2 + 7x2 – 35x + 56
dy/dx = 5x4 – 20x3 + 45x2 – 52x + 11
Answer is always same what-so-ever method we use.
问题 18. 如果 u、v 和 w 是 x 的函数,则证明
解决方案:
Let y = u.v.w.
Method 1: Using product Rule
Method 2: Using logarithmic differentiation
Taking log on both sides
log y = log u + log v + log w
Now, Differentiating w.r.t. x