Selina solutions

Grade 7

# Question 1

Q1) Multiply:

(i) 3x,\ 5x^2y\ and\ 2y

(ii) 5,\ 3a\ and\ 2ab^2

(iii) (iii) 5x + 2y and 3xy

(iv) 6a - 5b and - 2a

(v) 4a + 5b and 4a - 5b (vi) 9xy+2y^2\ and\ 2x-3y

(vii) -3m^2n\ +5mn-4mn^2and\ 6m^2n

(viii) 6xy^2-7x^2y^2+10x^3and\ -3x^2y^3

Solution 1:

(i) 3x,\ 5x^2y\ and\ 2y

= 3x\times5x^2y\times2y

= 15x^3y\times2y

= 30x^3y^2

(ii) 5,\ 3a\ and\ 2ab^2

= 5\times3a\times2ab^2

= 15a\times2ab^2

= 30a^2b^2

(iii) 5x + 2y and 3xy

= 3xy × (5x + 2y)

= 15x^2y+6xy^2

(iv) 6a - 5b and - 2a

= -2a × (6a - 5b)

= -12a^2+10ab

(v) 4a + 5b and 4a - 5b

(vi) 9xy+2y^2\ and\ 2x-3y

(vii) -3m^2n\ +5mn-4mn^2and\ 6m^2n

=6m^2n\left(-3m^2n+5mn-4mn^2\right)

= 18m^4n^2+30m^3n^2-24m^3n^3

(viii) 6xy^2-7x^2y^2+10x^3and\ -3x^2y^3

= 3x^2y^3\left(6xy^2-7x^2y^2+10x^3\right)

= -18x^3y^5+21x^4y^5-30x^5y^3

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