Question

Q6. Using suitable identity find the following products :

(i) (2x + 5 )(2 x + 6 )

(ii) 79 x 81​

Answer 1

Answer:

$\blue{\sf{(i) \: \: (2x + 5)(2x + 6)}}$

$\red {\sf{identity \: used \ \: : }}$

$\sf(x + a)(x + b) = {x}^{2} + x(a + b) + ab$

$\sf \underline{solution \ \: : }$

$\sf \to {2x}^{2} + 2x(5 + 6) + (5 \times 6)$

$\sf \to4 {x}^{2} + 2x(11) + (30)$

$\purple{\boxed{ \sf{{4 {x}^{2} + 22x + 30 }}}}$

$\blue{ \sf{(ii) \: \: 79 \times 81}}$

$\red {\sf{identity \: used \ \: : }}$

$\sf(x - y)(x + y) = ({x})^{2} - ({y})^{2}$

$\sf \underline{solution \ \: : }$

$\sf \to(80 - 1)(80 + 1)$

$\sf \to {(80)}^{2} - {(1)}^{2}$

$\sf \to6400 - 1$

$\purple{\boxed{ \sf{{6399 }}}}$

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