# Question Video: Subtraction of Two Algebraic Expressions Mathematics • 7th Grade

Find π΄ β π΅, given π΄ = 5π₯Β³ β 3π₯ and π΅ = β6π₯Β² + 3π₯.

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### Video Transcript

Find π΄ minus π΅, given π΄ is equal to five π₯ cubed minus three π₯ and π΅ is equal to negative six π₯ squared plus three π₯.

In order to answer this question, we need to subtract negative six π₯ squared plus three π₯ from five π₯ cubed minus three π₯. Before we start, itβs important to remember that we can only collect or group terms with the same exponent or power.

In this case, the only terms we can group together are negative three π₯ and positive three π₯. We also need to remember our rules when two signs are touching. If we have two positive signs, the resultant sign is a positive one or an addition sign. When we have a positive and a negative sign, in either order, our resultant sign is a negative or subtraction sign. And when we have two negative signs, the resultant sign is positive or addition.

The only term with π₯ cubed in it is the first one, five π₯ cubed. So this too must be in our answer. We have a negative six π₯ squared term. However, this term is being subtracted. In other words, we have negative negative six π₯ squared. Two negatives become a positive. Therefore, this is the same as six π₯ squared or positive six π₯ squared.

Finally, we need to group the π₯ terms, negative three π₯ minus positive three π₯. This time, our sign will become a subtraction or negative sign. So weβre left with negative three π₯ minus three π₯. Negative three minus three is equal to negative six. Therefore, negative three π₯ minus three π₯ equals negative six π₯.

This means that if π΄ is equal to five π₯ cubed minus three π₯ and π΅ is equal to negative six π₯ squared plus three π₯, then π΄ minus π΅ equals five π₯ cubed plus six π₯ squared minus six π₯.