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Let $f(x) = 3x^2 + x$ - HSC - SSCE Mathematics Extension 1 - Question 2 - 2001 - Paper 1

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Let-$f(x)-=-3x^2-+-x$-HSC-SSCE Mathematics Extension 1-Question 2-2001-Paper 1.png

Let $f(x) = 3x^2 + x$. Use the definition $$f'(a) = rac{f(a + h) - f(a)}{h}$$ to find the derivative of $f(x)$ at the point $x = a$. (i) Find $\int \frac{e^x}{1+... show full transcript

Worked Solution & Example Answer:Let $f(x) = 3x^2 + x$ - HSC - SSCE Mathematics Extension 1 - Question 2 - 2001 - Paper 1

Step 1

Let $f(x) = 3x^2 + x$. Use the definition to find the derivative of $f(x)$ at the point $x = a$.

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Answer

To find the derivative using the limit definition:

f(a)=limh0f(a+h)f(a)hf'(a) = \lim_{h \to 0} \frac{f(a + h) - f(a)}{h}

Calculate:

  1. f(a+h)=3(a+h)2+(a+h)=3(a2+2ah+h2)+a+h=3a2+6ah+3h2+a+hf(a + h) = 3(a + h)^2 + (a + h) = 3(a^2 + 2ah + h^2) + a + h = 3a^2 + 6ah + 3h^2 + a + h.
  2. f(a)=3a2+af(a) = 3a^2 + a.
  3. Therefore,

f(a)=limh0(3a2+6ah+3h2+a+h)(3a2+a)h=limh06ah+3h2+hhf'(a) = \lim_{h \to 0} \frac{(3a^2 + 6ah + 3h^2 + a + h) - (3a^2 + a)}{h} = \lim_{h \to 0} \frac{6ah + 3h^2 + h}{h}

  1. This simplifies to:

f(a)=limh0(6a+3h+1)=6a+1.f'(a) = \lim_{h \to 0} (6a + 3h + 1) = 6a + 1.

Step 2

Find $\int \frac{e^x}{1+e^x} dx$.

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Answer

To evaluate this integral, use the substitution u=1+exu = 1 + e^x, hence du=exdxdu = e^x dx.

Then the integral becomes:

1udu=lnu+C=ln1+ex+C.\int \frac{1}{u} du = \ln |u| + C = \ln |1 + e^x| + C.

Step 3

Find $\int_0^2 3 \cos x dx$.

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Answer

Evaluate this integral as follows:

3cosxdx=3sinx+C.\int 3 \cos x dx = 3 \sin x + C.

Apply the limits:

[3sinx]02=3sin(2)3sin(0)=3sin(2).\left[3 \sin x\right]_0^2 = 3 \sin(2) - 3 \sin(0) = 3 \sin(2).

Step 4

How many arrangements of the letters in the word ALGE BRAIC are possible?

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Answer

The word 'ALGE BRAIC' has 9 letters with A occurring twice and I occurring twice.

The formula for arrangements is:

n!n1!n2!,\frac{n!}{n_1! \cdot n_2!}, where nn is the total number of letters, n1n_1 and n2n_2 are the counts of respective repeated letters.

Thus:

9!2!2!=3628804=90720.\frac{9!}{2! \cdot 2!} = \frac{362880}{4} = 90720.

Step 5

How many arrangements of the letters in the word ALGE BRAIC are possible if the vowels must occupy the 2nd, 3rd, 5th and 8th positions?

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Answer

The vowels A, A, E, I need to occupy positions 2, 3, 5, and 8. The arrangements of the vowels:

4!2!=12.\frac{4!}{2!} = 12.

The remaining consonants L, G, B, R, C can occupy the remaining 5 positions:

5!=120.5! = 120.

Therefore, the total arrangements is:

12×120=1440.12 \times 120 = 1440.

Step 6

Find the term independent of $x$ in the binomial expansion of $(x^2 - 1)^9$.

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Answer

Using the binomial theorem, the general term is given by:

Tk=(nk)(x2)nk(1)k=(9k)x2(nk)(1)k.T_k = \binom{n}{k} (x^2)^{n-k} (-1)^k = \binom{9}{k} x^{2(n-k)}(-1)^k.

We seek the term where the exponent of xx is zero:

2(nk)=0nk=0k=9.2(n-k) = 0 \Rightarrow n-k = 0 \Rightarrow k = 9.

Thus, we find the term:

inom{9}{9}(-1)^9 = -1.

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