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### Course: Algebra basics>Unit 2

Lesson 3: Writing algebraic expressions

# Writing expressions with variables & parentheses

In this math lesson, we learned about expressions and how to simplify them step by step. We explored adding and multiplying expressions, like negative numbers and variables. By practicing these skills, we can solve more complex algebra problems with ease and confidence. Created by Sal Khan.

## Want to join the conversation?

• in the first problem why did he know to multiply -5+4x from the word product?
• Hi Valentina, I know it's late but i will answer in case if anyone has the same question. Sal knew because product/times stands for multiplication. Let's consider I have a expression 2 + 5, the product of 4 and that expression means 4*(2 + 5). Other more simple example could be, the product of 2 and 5 means 2 * 5 which is the same as saying 2 times 5. Hope it helps.
• at Salman says 4+(2*(7-2x)). Can't he just say 4+2(7-2x)?
• according to the PEMDAS order of operations,both will work :)
• Would it be better, instead of 4+(2·(7-2x)), to answer with 4+2·(7-2x) or, even better yet, 4+2(7-2x)? It seems that the extraneous parenthesis in the video answer might get marked wrong in many classrooms.
• Hi Dale! Yes, technically it would be a bit easier to remove the parenthesis in the case of the Order of Operations, but for some people who get confused, it's better to have a reminder to do the things in parenthesis first. Hope this clears up any problems!
• When you got the answer for the first question,shouldn't the answer be simplifies further to -34+32x? Why did you just leave it like that without simplifying. Wouldn't you get points off on a test or quiz grade?
• well, 34+ 32x is in simplest form, because you don't know the value of x.
• how does 7+-2x==7-2x,how do we drop the + sign?
• How would you write half of 14 in an algebraic expression
• To write anything as a fraction of itself (e.g. half of 14, one third of 6, e.t.c) , you will just need to multiply the number you're dividing by the numerator (e.g. half of 14 = 1/2*14=14/2=7)
• How would 7+ -2x be the same as 7- 2x ?
• I'm confused about when it says quantity. I think it just means to solve the problem or is there another definition?
• "The quantity of 4 times x" just means 4x. This wording is used because the value of x is currently unknown.
• For the last question, couldn't we have written the answer in this way 4+2(7-2x)?