CHAPTER 8

ALGEBRAIC EXPRESSIONS AND IDENTITIES

Exercise 8.3

1. Carry out the multiplication of the expressions in each of the following pairs:
(i) \(4p, q + r\)

\[ 4p \times (q + r) = 4p \times q + 4p \times r = 4pq + 4pr \]

Final answer: \(4pq + 4pr\)
(ii) \(ab, a - b\)

\[ ab \times (a - b) = ab \times a - ab \times b = a^2b - ab^2 \]

Final answer: \(a^2b - ab^2\)
(iii) \(a + b, 7a^2b^2\)

\[ (a + b) \times 7a^2b^2 = a \times 7a^2b^2 + b \times 7a^2b^2 \] \[ = 7a^3b^2 + 7a^2b^3 \]

Final answer: \(7a^3b^2 + 7a^2b^3\)
(iv) \(a^2 - 9, 4a\)

\[ (a^2 - 9) \times 4a = a^2 \times 4a - 9 \times 4a = 4a^3 - 36a \]

Final answer: \(4a^3 - 36a\)
(v) \(pq + qr + rp, 0\)

\[ (pq + qr + rp) \times 0 = 0 \]

Final answer: \(0\)
2. Complete the table:
First expression Second expression Product
\(a\) \(b + c + d\) \( = ab + ac + ad\)
\(x + y - 5\) \(5xy\) \( = 5x^2y + 5xy^2 - 25xy\)
\(p\) \(6p^2 - 7p + 5\) \(= 6p^3 - 7p^2 + 5p\)
\(4p^2q^2\) \(p^2 - q^2\) \( = 4p^4q^2 - 4p^2q^4\)
\(a + b + c\) \(abc\) \( = a^2bc + ab^2c + abc^2\)
3. Find the product:
(i) \((a^2) \times (2a^{22}) \times (4a^{26})\)

\[ a^2 \times 2a^{22} \times 4a^{26} \] \[ = 2 \times 4 \times a^{2+22+26} \] \[ = 8a^{50} \]

Final answer: \(8a^{50}\)
(ii) \(\left(\frac{2}{3}xy\right) \times \left(-\frac{9}{10}x^2y^2\right)\)

\[ \frac{2}{3}xy \times \left(-\frac{9}{10}x^2y^2\right) \] \[ = \frac{2}{3} \times \left(-\frac{9}{10}\right) \times x^{1+2} \times y^{1+2} \] \[ = -\frac{18}{30}x^3y^3 = -\frac{3}{5}x^3y^3 \]

Final answer: \(-\frac{3}{5}x^3y^3\)
(iii) \(\left(-\frac{10}{3}pq^3\right) \times \left(\frac{6}{5}p^3q\right)\)

\[ -\frac{10}{3}pq^3 \times \frac{6}{5}p^3q \] \[ = -\frac{10}{3} \times \frac{6}{5} \times p^{1+3} \times q^{3+1} \] \[ = -\frac{60}{15}p^4q^4 = -4p^4q^4 \]

Final answer: \(-4p^4q^4\)
(iv) \(x \times x^2 \times x^3 \times x^4\)

\[ x \times x^2 \times x^3 \times x^4 = x^{1+2+3+4} = x^{10} \]

Final answer: \(x^{10}\)
4. (a) Simplify \(3x(4x - 5) + 3\) and find its values for (i) \(x = 3\) (ii) \(x = \frac{1}{2}\)

First, simplify the expression:

\[ 3x(4x - 5) + 3 = 12x^2 - 15x + 3 \]

(i) When \(x = 3\):

\[ 12(3)^2 - 15(3) + 3 = 12 \times 9 - 45 + 3 \] \[ = 108 - 45 + 3 = 66 \]

(ii) When \(x = \frac{1}{2}\):

\[ 12\left(\frac{1}{2}\right)^2 - 15\left(\frac{1}{2}\right) + 3 \] \[ = 12 \times \frac{1}{4} - \frac{15}{2} + 3 \] \[ = 3 - 7.5 + 3 = -1.5 \]

Final answers: (i) \(66\), (ii) \(-1.5\)
(b) Simplify \(a(a^2 + a + 1) + 5\) and find its value for (i) \(a = 0\), (ii) \(a = 1\), (iii) \(a = -1\)

First, simplify the expression:

\[ a(a^2 + a + 1) + 5 = a^3 + a^2 + a + 5 \]

(i) When \(a = 0\):

\[ (0)^3 + (0)^2 + (0) + 5 = 5 \]

(ii) When \(a = 1\):

\[ (1)^3 + (1)^2 + (1) + 5 = 1 + 1 + 1 + 5 = 8 \]

(iii) When \(a = -1\):

\[ (-1)^3 + (-1)^2 + (-1) + 5 \] \[ = -1 + 1 - 1 + 5 = 4 \]

Final answers: (i) \(5\), (ii) \(8\), (iii) \(4\)
5. (a) Add: \(p(p - q), q(q - r)\) and \(r(r - p)\)

\[ p(p - q) + q(q - r) + r(r - p) \] \[ = p^2 - pq + q^2 - qr + r^2 - rp \]

\[ = p^2 + q^2 + r^2 - pq - qr - rp \]

Final answer: \(p^2 + q^2 + r^2 - pq - qr - rp\)
(b) Add: \(2x(z - x - y)\) and \(2y(z - y - x)\)

\[ 2x(z - x - y) + 2y(z - y - x) \] \[ = 2xz - 2x^2 - 2xy + 2yz - 2y^2 - 2xy \]

\[ = -2x^2 - 2y^2 + 2xz + 2yz - 4xy \]

Final answer: \(-2x^2 - 2y^2 + 2xz + 2yz - 4xy\)
(c) Subtract: \(3l(l - 4m + 5n)\) from \(4l(10n - 3m + 2l)\)

First, expand both expressions:

\[ 4l(10n - 3m + 2l) = 40ln - 12lm + 8l^2 \]

\[ 3l(l - 4m + 5n) = 3l^2 - 12lm + 15ln \]

Now subtract:

\[ (40ln - 12lm + 8l^2) - (3l^2 - 12lm + 15ln) \]

\[ = 40ln - 12lm + 8l^2 - 3l^2 + 12lm - 15ln \]

Group like terms:

\[ (8l^2 - 3l^2) + (-12lm + 12lm) + (40ln - 15ln) \]

\[ = 5l^2 + 0 + 25ln = 5l^2 + 25ln \]

Final answer: \(5l^2 + 25ln\)
(d) Subtract: \(3a(a + b + c) - 2b(a - b + c)\) from \(4c(-a + b + c)\)

First, expand both expressions:

\[ 4c(-a + b + c) = -4ac + 4bc + 4c^2 \]

\[ 3a(a + b + c) - 2b(a - b + c) \] \[ = 3a^2 + 3ab + 3ac - 2ab + 2b^2 - 2bc \]

\[= 3a^2 + ab + 3ac + 2b^2 - 2bc \]

Now subtract:

\[ (-4ac + 4bc + 4c^2) - (3a^2 + ab + 3ac + 2b^2 - 2bc) \]

\[ = -4ac + 4bc + 4c^2 - 3a^2 - ab - 3ac - 2b^2 + 2bc \]

Group like terms:

\[ = -3a^2 - 2b^2 + 4c^2 - ab + (-4ac - 3ac) + (4bc + 2bc) \]

\[ = -3a^2 - 2b^2 + 4c^2 - ab - 7ac + 6bc \]

Final answer: \(-3a^2 - 2b^2 + 4c^2 - ab - 7ac + 6bc\)

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