Question

expand using suitable identity ( 2x+3y+4z)2

Answer 1

Use this identity: 
$(a+b+c)^{2} = a^{2} + b^{2} + c^{2} + 2ab + 2bc + 2ca$

$(2x + 3y + 4z)^{2}$
$= (2x)^{2} + (3y)^{2} + (4z)^{2} + 2(2x)(3y) + 2(3y)(4z) + 2(4z)(2x)$
$=$$2^{2}x^{2} + 3^{2}y^{2} + 4^{2}z^{2} + 2*2*3*x*y + 2*3*4*y*z + 2*4*2*z*x$
$= 4x^{2} + 9y^{2} + 16z^{2} + 12xy + 24yz + 16xz$

If you are not able to understand related to this, then you can ask me in the comments. 

Hope this may help you. 

Answer 2

Question: if (2,0) is a solution of the linear equation 2x +3 y= k , then value of 'k' is (a) 3 (b) 6 (c) 5 (d) 2

Answer: since (2,0) is a solution of the give linear equation 2x+3y=I, then put x=2 and y=0 in the equation.

= 2(2) +3(0) =k =) k=4

Hence, the value of k is 4.