The red line is an increase in the money supply. The money supply is determined by the central bank and is a vertical line. The new equilibrium point is the black asterisk point. The income level remains unchanged at y1, but the interest rate drops. Reflected in Figure b, LM wants the asterisk point to move downward.

Money demand L=aY-bi (a and b are both positive, that is, positive with output and reverse with interest rate), the supply is given as S, and the equilibrium state is S= L=aY-bi, i=(aY-S)/b=(a/b)*Y-S/b, that is, the so-called LM curve slopes from the lower left to the upper right.

Extended information:

The LM curve represents the trajectory of various combinations of income and interest rates in the money market when money supply equals money demand. The mathematical expression of the LM curve is M/P=KY-HR, and its slope is positive.

The LM curve is a curve described by different combinations of income and equilibrium interest rates that keep the money market in equilibrium. In other words, on the LM curve, each point represents a combination of income and interest rates. These combination points just make the money market in equilibrium.

Baidu Encyclopedia-LM Curve