Question

(9х-3) (9х+3) - 81 х² - 39 при х=80

Answer 1

81x^2-9-81x^2-39=-9-39=-48
81x^2 и -81x^2 сокращаются 

Answer 2

To find the value of the expression (9x-3)(9x+3) - 81x^2 - 39 when x = 80, we can simply substitute the value of x and then evaluate the expression. Let's do that step by step:

Step 1: Substitute x = 80 in the expression: (9 * 80 - 3)(9 * 80 + 3) - 81 * 80^2 - 39

Step 2: Perform the calculations inside the parentheses: (720 - 3)(720 + 3) - 81 * 6400 - 39

Step 3: Continue evaluating the expression: (717)(723) - 81 * 6400 - 39

Step 4: Multiply the values inside the parentheses: 517491 - 81 * 6400 - 39

Step 5: Perform the multiplication: 517491 - 518400 - 39

Step 6: Subtract the values: -909

So, when x = 80, the expression (9x-3)(9x+3) - 81x^2 - 39 evaluates to -909.