Question

what is microeconomics and Keynesian economics? Please explain

Answer 1

Microeconomics
Microeconomics relates to the study of small units of economy separately under the assumption of Ceteris Paribus (other things remaining constant). Along the lines of partial equilibrium theory, microeconomics assesses the working of different parts of economy individually and consider them working under presumed uniformity that ultimately work to create equilibrium such determination of price level through quantity theory, the determination of interest rate, equilibrium in the labour markets and separate theory of firms etc.
It is interesting to note that classical economics is based on the foundations of microeconomics made so vibrant under partial equilibrium theory. It was the assumption of  flexibility of wages and prices that made the classicals believe that even if the units may sometimes fall into disequilibrium, but the economy will soon reach the natural full employment state.
However, the Great Depression during 1930s brought classical micro economic analysis under reconsideration with huge unemployment and low growth and forced the economists to think differently.

Keynesian Economics
One economist who thought so differently that his evaluation of economy brought a revolution in the field of economics. In his book "The General theory of Employment, interest and Money" 1936, Keynes laid the foundations of Macroeconomics.

Keynesian economics ( macro) relates to the study of economic variables as a whole intricate system rather than treating them individually. Along the lines of General equilibrium, Keynesian economics work to combine the determination of major variables like price level, interest rate, output and employment etc into one whole system and seek their effects on growth, inflation and employment. Since the classical microeconomic theory could not explain why there was disequilibrium in the economy during Great Depression, Keynesian macroeconomics explained that full employment state is rather rare and the economy may come in the habit of experiencing disequilibrium. In this case, counter cyclical fiscal policy of increased government expenditure and tax cuts would stimulate the economy by boosting aggregate demand and that economy may sometimes find itself below full employment level.