1) 3x square-4x+7

2) 4x square-5x+6
3) 2x square-4x+3

To evaluate these quadratic expressions, you need to substitute a value for the variable 'x' and perform the mathematical operations.

Let's evaluate each expression one by one:

1) 3x^2 - 4x + 7:

To evaluate this expression, you can substitute a value for 'x' and simplify the expression by following the order of operations (PEMDAS/BODMAS). For example, let's substitute x = 2:

3(2)^2 - 4(2) + 7

Simplifying the expression:

3(4) - 8 + 7

12 - 8 + 7

4 + 7

= 11

So, when x = 2, the value of the expression 3x^2 - 4x + 7 is 11.

2) 4x^2 - 5x + 6:

Similarly, let's substitute x = 3:

4(3)^2 - 5(3) + 6

4(9) - 15 + 6

36 - 15 + 6

21 + 6

= 27

So, when x = 3, the value of the expression 4x^2 - 5x + 6 is 27.

3) 2x^2 - 4x + 3:

Let's substitute x = 1/2:

2(1/2)^2 - 4(1/2) + 3

2(1/4) - 2 + 3

1/2 - 2 + 3

= 2.5

So, when x = 1/2, the value of the expression 2x^2 - 4x + 3 is 2.5.

Remember, you can always choose a different value for 'x' to evaluate these expressions.