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Changing the subject Changing the subject of a formula When a formula to find a given quantity is written, the subject of the formula is the letter which is on its own. Example A = r2 - Subject A V=lwh - Subject V To change the subject of a formula, we need to re-arrange the parts of the formula to leave a different letter as the subject. Remember: To move any term from one side of the equals sign in a formula or equation means that the sign is changed. If there is a choice of terms to be moved we usually move the add/subtract terms first. However, we cannot always rely on this rule and we just have to be careful to inspect the equation given. Make z the subject of the following formula: 1. Gz = H H z =G 2. 8z + T = Y 8z = Y – T z = Y- T 8 Gxz=H 3. Lz = Y2 – h 2- h Y z= L Complete Exercise 4 Questions 1 – 30 Formula with x2 and negative x terms When a formula contains an x2 term that needs to be the subject we must • Leave the x2 term on its own first and, • Then square root the other side to make x the subject. Example ax2 = r – t x2 = r a- t x = r a- t When a formula contains a negative x term that is going to be the new subject • Move the x term to the other side to make it positive, • Then make it the subject by leaving it on its own Example h – bx = m h = m + bx h – m = bx h-m = x b