Boyle's Law: The relationship between a gas' volume and pressure, where the temperature is assumed to be constant. The relationship is an inverse one and the formula is P₁V₁ = P₂V₂
Charles' Law: The relationship between a gas' volume and temperature, where pressure is assumed to be constant. The relationship is a linear one and the formula is V₁ ÷ T₁ = V₂ ÷ T₂.
Gay-Lussac's Law: The relationship between temperature and pressure, where volume is assumed to be constant. The relationship is a linear one and the formula is P₁ ÷ T₁ = P₂ ÷ T₂.
Combined Law: Boyle's, Charles', and Gay-Lussac's laws all combined, where all the variables are changing. I'm unsure of what the relationship is but the formula is P₁V₁/T₁ = P₂V₂/T₂.
*Note: The subscripts just indicate the original amount to the new amounts.
