Any of these three adjectives can be used to express a positive and hopeful attitude towards a situation.
Yo u could also use the word "certain" to express your confidence or lack of doubt that something will happen.
In the first sentence, you have used the adverb 'extremely'. 'Extremely' is an adverb from the adjective 'extreme', which means 'reaching a high or the highest degree; very great'. By saying, I am extremely optimistic', you are actually saying that you are optimistic to the highest degree.
In the second sentence, you have said that you are 'cocksure'. The adjective 'cocksure' has several meanings. But, in this context, it means 'absolutely sure or certain'
最初の表現では'extremely'と言う副詞を使っています。
'Extremely' とは'extreme'と言う形容詞の副詞の形で、極めて、非常にという様な意味になります。
'I am extremely optimistic'と言うと、あなたは非常に楽観的だという意味になります。
2つ目の表現では 'cocksure'を使っています。この形容詞'cocksure' はいくつかの意味がありまが、ここでは確実にや間違いなくと言う意味になりす。
---> If you are positive about things, you are hopeful and confident, and think of the good aspects of a situation rather than the bad ones.
---> Someone who is optimistic is hopeful about the future or the success of something in particular.
Be positive about your future and get on with living a normal life.
You really must try to start thinking positively.
Michael was in a jovial and optimistic mood.
I am hugely optimistic for the future.
--->positiveは、hopeful（人助けをする優しい人）でconfident（自信のある）、そして状況を悪い方向よりもいい方向で捉える人のことを表す時に言います。
---> optimistic は、特に将来の成功を特に希望的に持っている人のことを言います。
Be positive about your future and get on with living a normal life.
将来にもっと自信を持って、普通の生活にうまくなれてね。
You really must try to start thinking positively.
ポジティブにもっと考えなよ。
Michael was in a jovial and optimistic mood.
マイケルは陽気で楽観的なムードだった。
I am hugely optimistic for the future.
僕は将来にすごく楽観的だよ。
When wanting to describe yourself as a positive thinking person, you can use "optimistic", "hopeful" or "positive outlook". "I have a positive outlook on life."
自分自身を前向きな考えの人だと表現したい時は、"optimistic", "hopeful"、または "positive outlook"を使うことができます。
例：
I have a positive outlook on life.
私は楽天的な人間です。
The two sentences you see provided above are excellent ways to express to your listener that you are very optimistic or positive. In the first sentence you will see the term look on the bright side of things and in the second sentence you will see the term glass half full. Both of these terms mean optimistic or cheery.
上記2つの例文は、非常に楽観的、或いは前向きであることを表現する素晴らしい言い方です。
最初の例文には、look on the bright side of thingsという表現があり、2番目の例文にはglass half fullという表現があります。どちらも「楽観的な、明るい」という意味です。
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