Algebraic Expressions and Polynomials

Option B states 4x + 5x = 8x², which is incorrect. When adding like terms 4x and 5x, we add the coefficients: 4x + 5x = 9x, not 8x². The other options A, C, and D all show correct algebraic expansions and simplifications.

A monomial is an expression consisting of a single term. xyz is a single term, so it is a monomial.

The constant term in an expression or equation has a fixed value and does not contain variables.
So, $-7$ is the constant term in the expression, $4x^2+5x^6-7x^2-7+2x^2-7x^6$

The variables are $x$ and $y$. Number of variables $=2$

variables in $(1)$ are $ x$ and $ y$ where as variables in $(2$) are $ x, y, z$.

Both the terms of the given expression have either $x$ or $y$ as the variable. 

Both the terms in the given expression contain atleast one variable, $x$ and $xy$..

The variables used are $x$ and $y$.

The constant term in an expression or equation has a fixed value and does not contain variables.
So, $-12$ is the constant term in the expression, $23x^3+12x^2-6x-12$.

General equation is $ax^3+bx^2+cx+d$ 

Given equation is $z^3+2z^2+5z+1$

$x^2+3x+5$
$=(2)^2+3\times 2+5$
$=4+6+5$
$=15$

$x^2+3x+5$
$=(-1)^2+3\times (-1)+5$
$=1-3+5$
$=6-3$
$=3$

The variables are $ x$,$ y$ and $z $