Formal language or academic is less personal than informal language. It is used when writing for professional or academic purposes like university assignments. Formal language does not use colloquialisms, contractions or first person pronouns such as 'I' or 'We'. Informal language is more casual and spontaneous.
Informal language is more casual and spontaneous. It is used when communicating with friends or family either in writing or in conversation. It is used when writing personal emails, text messages and in some business correspondence. The tone of informal language is more personal than formal language.
The thesis relates to your supporting evidence because you are stating what you want to say in your thesis and your supporting evidence backs up your thesis.
