Idea 16of 23Builds onSolve it on the balance
Put it back to check
How can you be sure a solution is right?
Today you'll discover
- how to test someone's answer
- what a wrong answer does to the balance
- why you never need an answer key
Think firstKai says x = 9 solves 2x + 5 = 21
Kai says x = 9. Is Kai right?
Decide first, then press Next. Put the answer back in and see if the pans stay level.
A pan balance with two boxes marked x and a 5 block on the left and a 21 block on the right. With 9 in each box the left is 2 × 9 + 5 = 23 and the pans tip. Taking 5 off both pans leaves two boxes against 16. With 8 in each box both sides are 21 and the pans are level. The last step shows 4x + 6 = 30.
See the whole ideathe big idea and the key word, in one place
The big idea
To check a solution, put it back in for the letter: both sides must match.
For exampleCheck x = 8 in 2x + 5 = 21: 2 × 8 + 5 = 16 + 5 = 21. Both sides are 21.
Easy to get wrongClose is not good enough: 23 and 21 do not match, so 9 is wrong.
Key word
- verify
- check that a solution works by putting it back into the equation
Ready to use it?
- Check whether a number solves an equation.